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https://doi.org/10.17508/CJFST.2018.10.2.10

Stability offrozen Nigerian soups as affected by freeze-thaw cycles

AKEEM OLAYEMI RAJI   ORCID icon orcid.org/0000-0002-4805-4943 ; Department of Food Science and Technology, College of Agriculture and Veterinary Medicine, Kwara State University, Malete, Ilorin, Nigeria
RAHMAN AKINOSO ; Department of Food Technology, University of Ibadan, Oyo State, Nigeria
UCHE IBANGA ; Federal College of Freshwater Fisheries Technology, New Bussa, Niger State, Nigeria
MONSURAT OYEWALE RAJI ; Department of Food Technology, University of Ibadan, Oyo State, Nigeria

Puni tekst: engleski, pdf (919 KB) str. 206-219 preuzimanja: 263* citiraj
APA 6th Edition
RAJI, A.O., AKINOSO, R., IBANGA, U. i RAJI, M.O. (2018). Stability offrozen Nigerian soups as affected by freeze-thaw cycles. Croatian journal of food science and technology, 10 (2), 206-219. https://doi.org/10.17508/CJFST.2018.10.2.10
MLA 8th Edition
RAJI, AKEEM OLAYEMI, et al. "Stability offrozen Nigerian soups as affected by freeze-thaw cycles." Croatian journal of food science and technology, vol. 10, br. 2, 2018, str. 206-219. https://doi.org/10.17508/CJFST.2018.10.2.10. Citirano 31.05.2020.
Chicago 17th Edition
RAJI, AKEEM OLAYEMI, RAHMAN AKINOSO, UCHE IBANGA i MONSURAT OYEWALE RAJI. "Stability offrozen Nigerian soups as affected by freeze-thaw cycles." Croatian journal of food science and technology 10, br. 2 (2018): 206-219. https://doi.org/10.17508/CJFST.2018.10.2.10
Harvard
RAJI, A.O., et al. (2018). 'Stability offrozen Nigerian soups as affected by freeze-thaw cycles', Croatian journal of food science and technology, 10(2), str. 206-219. https://doi.org/10.17508/CJFST.2018.10.2.10
Vancouver
RAJI AO, AKINOSO R, IBANGA U, RAJI MO. Stability offrozen Nigerian soups as affected by freeze-thaw cycles. Croatian journal of food science and technology [Internet]. 2018 [pristupljeno 31.05.2020.];10(2):206-219. https://doi.org/10.17508/CJFST.2018.10.2.10
IEEE
A.O. RAJI, R. AKINOSO, U. IBANGA i M.O. RAJI, "Stability offrozen Nigerian soups as affected by freeze-thaw cycles", Croatian journal of food science and technology, vol.10, br. 2, str. 206-219, 2018. [Online]. https://doi.org/10.17508/CJFST.2018.10.2.10

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Sažetak
The freezing and defrosting of frozen soups is a known practice among Nigerians and their stability is of utmost concern. Standard recipes were used to prepare selected traditional soups (‘ila’, ‘ogbono’, ‘ewedu’ and ‘kuka’ soups) of Nigerian origin. The influence of packaging materials (aluminium and plastics) and thawing conditions (microwave oven, ambient condition and hot water thawing) on the soups were determined by freezing them at -20 °C and thawing at the above conditions for four cycles at an interval of 5 days. At the end of each cycle, the free fatty acid, peroxide value, pH value, titratable acidity, viscosity, total plate counts and sensory attributes of the samples were determined using standard methods. Free fatty acid, peroxide value, pH, titratable acidity, viscosity and total plate counts of soups ranged from 0.56-3.09%, 5.82-14.54 mEq/kg, 6.53-7.17, 0.07-1.41%, 0.81-2.00 Pa·s and 1.50-2.92Log CFU/mL respectively. The nature of packaging materials and thawing conditions significantly influenced the stability indices of the soups at p<0.05. Limited deteriorative changes were observed in microwave-thawed soups in plastic containers, and were mostly preferred by panelists. The soups stability cannot be guaranteed if the number of cycle is above three, because of deteriorative increase in free fatty acid and peroxide values.

Ključne riječi
Nigerian soups; freezing; thawing; sensory properties; storage stability

Hrčak ID: 210842

URI
https://hrcak.srce.hr/210842

▼ Article Information



Introduction*

Freezing is one of acceptable preservation methods used to extend the shelf life of food for a relatively long period of time (Pietrasik and Janz, 2009). The freezing process reduces the temperature of the food product generally below −18 °C, which crystallize as part of the free water and concentrates of some of the solutes (Leygonie et al., 2012). Freezing and frozen storage reduces the food quality, but the rate of quality loss can be minimized if the process is carefully controlled (Nilgun et al., 2013). During freezing, the activities 
of most of the pathogenic microorganisms 
are seized in frozen state to prevent spoilage 
(Bing and Da-wen, 2002). The nature of ice formed during freezing, the storage temperature, the packaging materials used and the physiology of the frozen mass have significant influence on the quality and safety of frozen food products (Torres and Canet, 2001). Even though freezing highly retains the quality of frozen food, quality deterioration still occurs at a slower rate during frozen storage. Therefore, a better understanding of the effects of frozen storage is of utmost importance to the food industry.

Thawing of frozen materials is of great concern in food processing, since the quality of frozen food is closely related to freezing and thawing processes. The rate of freezing and size of ice crystals formed during freezing are of utmost importance for reduction of tissue damage and drip loss during thawing (Bing and Da-wen, 2002). Thawing process induces chemical changes and physical damage to foods. Therefore, thawing time ought to be minimal to limit microbial proliferation, chemical deterioration and excessive loss of water caused by dripping or dehydration (Taher and Farid, 2001).

Traditional foods are extremely health protective and nutrient rich, some have been reported to possess high proteins, important fats like omega-3 fatty acids and antioxidants (Kpikpi et al., 2009; Amadi et al., 2011). Nigeria is made of many tribes, having completely different traditional soups that are endemic to different ethnic groups and tribes. Dietary staple foods obtained from majorly cereals and tubers are consumed with the soups and each tribe has developed their different local dishes from cereals and tubers cultivated within their locality (Raji et al., 2016). However, repetitive freezing of soups after use as being practiced in modern homes has been reported as a better alternative to traditional periodical heating of soups after use, which results in losses of vitamins (Raji et al., 2015). This research work was carried out because literature is sparse on the stability, microbial safety and sensory properties of some freeze-thawed Nigerian soups.

Materials and methods

Preparation of soups

Chosen soups were prepared in accordance with the standard recipe (Table 1) described by FIIRO (2006).

Table 1 The list of ingredients used for preparation of soups
Ogbono Ewedu Ila Kuka
Bitter Leaf(20 g) Leaves(120 g) Okro(fruit(640g)) Meat (1000 g)
Ogbono (ground (240 g)) Egusi(ground(40 g)) Pepper(14 g) Onion (75 g)
Palm oil (80 mL) Water (500 mL) Ugwu(200 g) Dry fish (50 g)
Water (2000 mL) Crayfish(40 g) Meat(1000 g) Stockfish(500 g)
Maggi (8 g) Potash(1 g) Crayfish(40 g) Kuka (Powder (150 g))
Onion (3400 g) Iru(5 g) Onion(300 g) Maggi (10 g)
Iru (locust beans (10 g)) Salt(5 g) Salt(14 g) Salt(8 g)
Fish(Smoked (310 g)) Palm oil(40 mL) Curry(3 g)
Meat(1000 g) Water(2000 mL) Thyme(1.4 g)
Crayfish(ground (40 g)) Maggi cube(8 g) Crayfish(30 g)
Periwinkle(deshelled (94 g)) Iru(locust beans(10 g)) Water(2000 mL)
Salt(10 g) Palm oil(100 mL)
Pepper(ground (14 g))

Preparation of Ogbono soup

Fish and meat were washed thoroughly before and after cutting them into pieces. The meat and fish were placed in clean pot containing sliced onions and considerable amount of water. The mixture was boiled until the meat softened. Crayfish, periwinkles pepper, oil and Ogbono (Irvingia gabonensis) ground seeds were added to the mixture. The mixture was gently stirred and allowed to boil over a medium heat for 5 minutes. Seasoning and chopped vegetable were added to the mixture and was allowed to simmer for 5 minutes. Prior to freezing, the soup was allowed to cool down and then packaged into different containers.

Preparation of Ewedu soup

The freshly detached Ewedu (Corchorus olitorus) leaves from the parent stalks were washed thoroughly to remove dirt. Blending of the leaves was done in a blender containing considerable amount of water. Small piece of potash was added into the pot containing the blended leaves and it was boiled for 5 minutes. While the pot was kept open, melon seeds powder was sprinkled into it. It was simmered and gently stirred for 5 minutes. Before heating was stopped, ground crayfish, locust bean and table salt were added to it. Prior to freezing, the soup was allowed to cool down and then packaged into different containers.

Preparation of Okro soup

Fish and meat were washed thoroughly before and after cutting them into pieces. They were placed in clean pot containing sliced onions and considerable amount of water. The mixture was boiled until the meat softened. Milled crayfish, pepper, and oil were added to the mixture. The mixture was gently stirred and it was allowed to boil over a medium heat for 10 minutes. Seasoning and chopped okro (Hibiscus esculentus) fruits were added to the boiling mixture. The mixture was then allowed to simmer until the meat, vegetable and okro tendered, and the required consistency was reached. The soup was allowed to cool down and then packaged into different containers prior to freezing.

Preparation of Miyan Kuka soup

The pieces of fresh meat bought from the market were washed and placed into a clean pot. Clean water and sliced onions were added to it. The mixture was heated for 25 minutes. Washed stockfish (Gadus morhua), curry, dried bonga fish (Ethmalosa fimbriata), ground pepper and water were added to the boiling mixture. It was further cooked for 20 minutes. Ground “kuka” (Adansonia digitata) leaves were added and it was gently stirred. The soup was allowed to steam for 15 minutes, to cool down and then it was packaged into different containers prior to freezing.

Freezing and thawing of soups

Freshly prepared soups packaged in aluminum and plastic containers (100 g each) were frozen and stored in a laboratory scale chest freezer (Scanfrost chest; Model SFL-111, Hangzhou, China). The frozen soups were stored at −20°C for 5 days before being thawed 
(cycle 1). Soups were repeatedly frozen and thawed for four cycles using the thawing methods described below in order to mimic the thawing and refreezing processes that frozen soups experienced when some portions are consumed in modern homes.

Thawing methods

The soups were thawed using three different thawing methods stated below.

Thawing in microwave oven

Thawing of soups was done in a microwave oven operated at frequency of 2.45 GHz (LG, MS2024W, 
450 W max. power) using defrost setting, until the temperature at the centre of the soups reached 0 oC. Temperature variation was monitored with the aid of digital thermometer with a probe inserted at the centre of the frozen mass.

Thawing in hot water

The frozen soups were thawed in a water bath containing boiling water (100 °C) until the temperature at the centre of the soups reached 0 °C. Temperature variation was monitored with the aid of digital thermometer with a probe inserted at the centre of the frozen mass.

Thawing at ambient temperature

The frozen soups were thawed at ambient temperature (28–32 °C) until the temperature at the centre of the soups reached 0 °C. Temperature variation was monitored with the aid of digital thermometer with a probe inserted at the centre of the frozen mass.

Determination of free fatty acid content

The analyses described below were carried out at the end of every freeze-thawed cycle to determine the stability of the selected soup samples.

The percentage of the free fatty acid (FFA) was calculated for the soup samples using AOAC (2005). 
1.0 g of soup sample was measured into 250 mL flask. 25 mL of alcohol and 1.0 mL of phenolphthalein indicator were added to it. The mixture was titrated with aqueous 0.5 N NaOH. The volume of NaOH 
used in the titration corresponded to the percentage of free fatty acid calculated, using equation 1:

CJFST-10-2-206-e1.jpg

The FFA figure was calculated as oleic acid (1 mL of 0.1 M sodium hydroxide = 0.0282 g oleic acid).

Peroxide value

Peroxide value was evaluated according to the method of AOAC (2005). Two grams of soup sample was weighed into a tube and 1 g of powdered Potassium iodide with 20 mL of solvent mixture (glacial acetic acid and chloroform) was added.This was then placed into boiling water for 30 s.The content was poured into a flask containing 20 mL of 5% iodide solution. The tube was then washed with 25 mL of distilled water and titrated with 0.002 N sodium thiosulphate solution using starch as indicator. A blank was prepared alongside with the soup sample. Peroxide value was obtained using the equation 2:

CJFST-10-2-206-e2.jpg

Where: V2 = Blank titre value, V1 = Sample (s) titre value

pH determination

The pH of each soup was evaluated using a Crison MicropH 2002 potentio-meter and axerolyt electrode In gold Lot 406-MG- DXK-57/25, that was calibrated at pH 4.0 and pH 7.0. The probe on the electrode was inserted into the test samples and the pH was read directly from the potential meter.

Titratable acidity

Each soup sample (5 g) was diluted with 200 mL of CO2 free distilled water inside the beaker, 1.0 mL of phenolphthalein indicator was added and then titrated with 0.1 M NaOH solution until pink colour was observed (AOAC, 2005).

Viscosity determination

The method described by Akusu and Kiin-Kabari (2013) was used to determine the viscosity of each soup. The viscosity of the soups was obtained at ambient temperature (30 ± 2 °C) with the aid of a rotary digital viscometer (NDJ – 85, China) with spindle number 3 at 30 rpm and read in Pa·s.

Microbial analyses

The microbiological analyses described below were carried out on the selected soups samples.

Total bacteria count

Conventional colony count method for the enumeration of bacteria in food was adopted as described by Jasson et al. (2010). Samples (1.00 mL/g) were taken from the soups. Decimal dilutions were performed for all the samples and 0.1 mL of 10-1 dilutions were inoculated on nutrient agar plates and incubated at 37 °C for 24h. After incubation, the colonies were counted by using colony counter (Subra Scientific Co., India). The final counts of colonies in petri dishes took into account the dilution factors depending on the seeded volume and dilution, thus providing the initial number of the cells. Analysis was replicated three times and the arithmetic mean was reported as the final result. Inactivation was expressed as Log N0/N, where N0 is the number of microorganisms initially contained in the fresh samples and N is the corresponding number of microorganisms after freezing and thawing.

Isolation procedure

Various colonies observed on the plates were examined for colonial differences using the method described by Fawole and Oso (1998). Representatives of different colonies were streaked on sterile nutrient and mac-conkey agars. Pure cultures resulting from the isolations were subcultured and preserved on agar slants.

The characterization of the colonies

The isolated bacteria were identified and characterized using the following morphological and biochemical tests:

Morphological test

Gram reaction and cell morphology of the isolates were examined from their heat fixed smears, using the methods described by Prescott et al. (2005).

Biochemical tests

Theoxidase, indole, catalase and coagulase tests were carried out on the isolates using the methods described by Prescott et al. (2005).

Fungi counts

The fungi count was determined using the method of Raper and Fennel (1973) as reported by Atanda et al. (2009). 1 mL of each sample was aseptically transferred into 9 mL distilled water and properly homogenized. The samples were subsequently decimally diluted. All samples were analysed in triplicate on potato dextrose agar containing 0.001% of chloraphenicol and allowed to incubate at ambient temperature (30°C±2) for 48h.

Sensory evaluation

The effect of freeze-thaw cycles on the sensory properties of the selected soups subjected to freezing and thawing conditions was tested at the end of the fourth cycle by comparing them with the freshly prepared soups. Twenty trained panelists were selected from the staff and students
(12 females and 8 males) of the Kwara State University, Malete, Nigeria on the basis of interest, availability and familiarity with the soups. The samples were coded with 3-figure random numbers and presented in random order to each panelist at ambient room conditions (25-30 °C). A 9-point hedonic scale (where 1 represents dislike extremely and 9 represent like extremely) was used by the panelists to score for colour, taste, aroma, consistency and overall acceptability of the soups.

Statistical analysis

All analyses were performed in triplicate. Data were subjected to a one-way analysis of variance (ANOVA) using Statistical Package for Social Sciences (SPSS) V. 17.0. Following ANOVA, means were separated using Duncan Multiple Range Test (DMRT) at 95% confidence level (p≤0.05).

Result and discussion

Degradative changes during freezing and refreezing of soup samples

The results of the free fatty acid, peroxide value, pH, titratable acidity and viscosity of the freeze-thawed soup samples were presented in Tables 2-6{ label needed for table-wrap[@id='t3'] }{ label needed for table-wrap[@id='t4'] }{ label needed for table-wrap[@id='t5'] }{ label needed for table-wrap[@id='t6'] }.

Table 2 The stability of free fatty acid in selected soups as affected by freeze-thaw cycles (%)
Sample Ogbono Ewedu Okro(Ila)             Kuka
Cycle 0
FP 1.70±0.01i 0.56±0.01i 1.13±0.01d          1.13±0.10j
Cycle 1
AH 1.77±0.06e-i 0.61±0.06i 1.21±0.02d     1.16±0.01g-j
AR 1.85±0.04ef 0.61±0.06i 1.22±0.10d     1.17±0.01g-i
AM 1.79±0.05e-i 0.61±0.05i 1.21±0.01d     1.16±0.00g-i
PH 1.74±0.06g-i 0.58±0.05i 1.16±0.00d     1.15±0.00h-j
PR 1.83±0.06e-g 0.61±0.07i 1.21±0.04d     1.18±0.01gh
PM 1.72±0.07hi 0.57±0.04i 1.14±0.02d     1.14±0.01ij
Cycle 2
AH 1.79±0.06e-i 0.80±0.02h 1.24±0.02d     1.16±0.01g-j
AR 1.86±0.04e 0.81±0.02h 1.25±0.01d     1.18±0.00gh
AM 1.81±0.06eh 0.81±0.01h 1.25±0.01d     1.17±0.01g-i
PH 1.76±0.05f-i 0.82±0.02h 1.27±0.02d     1.16±0.01g-j
PR 1.86±0.03e 0.83±0.02h 1.27±0.04d     1.18±0.01g
PM 1.73±0.06hi 0.77±0.05h 1.19±0.07d     1.15±0.01h-j
Cycle 3
AH 2.28±0.06b-d 1.99±0.05g 2.71±0.08c     2.21±0.02ef
AR 2.35±0.02ab 2.06±0.02fg 2.81±0.13bc     2.26±0.01a-c
AM 2.31±0.05a-c 2.06±0.02fg 2.79±0.22bc     2.24±0.03c-e
PH 2.22±0.07d 2.10±0.01f 2.79±0.42bc     2.22±0.01ef
PR 2.35±0.04ab 2.33±0.06e 3.02±0.42ab     .28±0.02a
PM 2.20±0.07d 1.99±0.01g 2.69±0.11c     2.21±0.01f
Cycle 4
AH 2.32±0.05a-c 2.38±0.08de 2.78±0.07bc     2.23±0.01d-f
AR 2.39±0.04a 2.41±0.02cd 2.83±0.06bc     2.27±0.01ab
AM 2.35±0.03ab 2.46±0.06bc 2.86±0.12bc     2.25±0.02b-d
PH 2.25±0.07cd 2.50±0.03b 2.90±0.11a-c     2.21±0.01ef
PR 2.39±0.02a 2.77±0.08a 3.09±0.32a     2.26±0.05a-c
PM 2.21±0.07d 2.39±0.04c-e 2.79±0.09bc     2.20±0.06f
Values are means of three replicates. Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly Prepared, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.
{ label needed for table-wrap[@id='t3'] }
Table 3 The stability of peroxide values in selected soups as affected by freeze-thawe cycles (meq/kg)
Sample Ogbono Ewedu Okro(Ila) Kuka
Cycle 0
FP 8.60±0.10g 7.17±0.05h 5.82±0.22e 6.09±0.09gh
Cycle 1
AH 8.88±0.29e-g 7.81±0.68gh 6.30±0.11e 6.15±0.05e-h
AR 9.30±0.20e 7.87±0.59g 6.36±0.05e 6.21±0.01e-h
AM 9.01±0.27e-g 7.80±0.51gh 6.30±0.47e 6.17±0.03e-h
PH 8.74±0.30fg 7.46±0.52gh 6.02±0.02e 6.11±0.03f-h
PR 9.19±0.29ef 7.81±0.70gh 6.30±0.23e 6.26±0.03ef
PM 8.66±0.33fg 7.35±0.48gh 5.94±0.12e 6.07±0.05h
Cycle 2
AH 9.02±0.30e-g 9.77±0.01fg 6.45±0.11e 6.15±0.06e-h
AR 9.35±0.12e 10.17±0.15ef 6.53±0.05e 6.25±0.04e-g
AM 9.12±0.29e-g 10.17±0.12ef 6.51±0.03e 6.20±0.06e-h
PH 8.84±0.26e-g 10.22±0.15ef 6.59±0.08e 6.15±0.05e-h
PR 9.36±0.13e 10.51±0.32e 6.62±0.20e 6.30±0.03e
PM 8.70±0.28fg 9.35±0.54g 6.20±0.35e 6.11±0.06f-h
Cycle 3
AH 13.91±0.36b-d 11.38±0.01d 11.68±0.41cd 9.80±0.07cd
AR 14.10±0.10a-c 12.13±0.12bc 12.17±0.45cd 10.10±0.10a
AM 14.09±0.29a-c 12.17±0.16bc 12.00±0.85cd 9.91±0.12bc
PH 13.52±0.42d 12.39±0.03b 11.90±1.31ab 9.76±0.07cd
PR 14.32±0.27ab 13.76±0.39a 13.18±1.31ab 10.08±0.07a
PM 13.42±0.44d 11.73±0.10cd 11.38±0.69d 9.73±0.12d
Cycle 4
AH 14.14±0.28a-c 12.04±0.39bc 11.98±0.48cd 9.80±0.11cd
AR 14.54±0.25a 12.19±0.02bc 12.03±0.28cd 10.00±0.08ab
AM 14.34±0.20ab 12.43±0.24b 12.31±0.44b-d 9.91±0.12bc
PH 13.73±0.43cd 12.62±0.10b 12.37±0.52bc 9.77±0.05cd
PR 14.53±0.13a 13.99±0.33a 13.57±1.03a 9.99±0.23ab
PM 13.46±0.40d 12.06±0.16bc 11.58±0.96cd 9.71±0.07d
Values are means of three replicates. Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly Prepared, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.
{ label needed for table-wrap[@id='t4'] }
Table 4 The stability of ph in selected soups as affected by freeze-thaw cycles
Sample Ogbono Ewedu Okro(Ila)             Kuka
Cycle 0
FP 7.10±0.10a 6.97±0.06ab 7.10±0.10a 7.17±0.06a
Cycle 1
AH 7.10±0.10a 7.00±0.00a 7.07±0.12ab 6.93±0.06b-d
AR 6.87±0.06c-e 6.87±0.06cd 6.87±0.06c-f 6.90±0.00b-e
AM 6.87±0.06c-e 6.87±0.06cd 6.87±0.06c-f 6.87±0.06c-f
PH 6.93±0.06bc 6.93±0.06a-c 6.93±0.06b-d 6.90±0.10b-e
PR 6.90±0.00b-d 6.93±0.06a-c 6.93±0.06b-d 6.87±0.06c-f
PM 7.10±0.00a 7.00±0.01a 7.10±0.10a 7.13±0.06a
Cycle 2
AH 7.00±0.00ab 7.00±0.00a 6.97±0.06a-c 6.87±0.06c-f
AR 6.73±0.06fg 6.77±0.06ef 6.73±0.06f-i 6.73±0.06e-i
AM 6.80±0.10d-f 6.77±0.06ef 6.80±0.10c-g 6.80±0.10c-g
PH 6.77±0.06e-g 6.77±0.06ef 6.77±0.06e-h 6.77±0.06d-h
PR 6.60±0.00hi 6.67±0.06gh 6.63±0.06h-j 6.60±0.00hi
PM 6.87±0.06c-e 6.90±0.00b-d 6.90±0.10c-e 7.07±0.06ab
Cycle 3
AH 6.77±0.06e-g 6.77±0.06ef 6.77±0.06e-h 6.70±0.10f-i
AR 6.57±0.06hi 6.63±0.06hi 6.63±0.06h-j 6.57±0.06i
AM 6.73±0.06fg 6.73±0.06fg 6.73±0.06f-i 6.73±0.06e-i
PH 6.73±0.06fg 6.73±0.06fg 6.73±0.06f-i 6.77±0.06d-h
PR 6.53±0.06i 6.63±0.06hi 6.57±0.06j 6.60±0.17hi
PM 6.83±0.06fg 6.87±0.06cd 6.90±0.10c-e 6.97±0.15bc
Cycle 4
AH 6.73±0.06fg 6.73±0.06fg 6.73±0.06f-i 6.73±0.06e-i
AR 6.53±0.06i 6.60±0.00hi 6.57±0.06j 6.60±0.17hi
AM 6.73±0.06fg 6.73±0.06fg 6.73±0.06f-i 6.73±0.06e-i
PH 6.67±0.06gh 6.67±0.06gh 6.67±0.06g-j 6.73±0.06e-i
PR 6.53±0.06i 6.57±0.06i 6.60±0.17ij 6.63±0.21g-i
PM 6.83±0.07c-f 6.83±0.06de 6.87±0.06c-f 6.93±0.06b-d
Values are means of three replicates. Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly Prepared, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.
{ label needed for table-wrap[@id='t5'] }
Table 5 The stability of titratable acidity in selected soups as affected by freeze-thaw cycles (%)
Sample Ogbono Ewedu Okro (Ila) Kuka
Cycle 0
FP 0.21±0.01g 0.11±0.01e 0.07±0.01g-i 0.07±0.01c
Cycle 1
AH 0.22±0.01e-g 0.11±0.01e 0.08±0.00f-i 0.08±0.00b
AR 0.23±0.01e 0.10±0.01e 0.08±0.00f-h 0.08±0.00b
AM 0.22±0.01e-g 0.11±0.01e 0.08±0.00f-i 0.08±0.00b
PH 0.22±0.01fg 0.10±0.01e 0.07±0.00hi 0.08±0.00b
PR 0.23±0.01ef 0.11±0.01e 0.08±0.00f-i 0.08±0.00b
PM 0.21±0.01fg 0.10±0.00e 0.07±0.00i 0.08±0.00b
Cycle 2
AH 0.22±0.01e-g 0.20±0.00d 0.08±0.00fg 0.08±0.00b
AR 0.23±0.01e 0.22±0.02d 0.08±0.00fg 0.08±0.00b
AM 0.23±0.01ef 0.20±0.00d 0.08±0.00fg 0.08±0.00b
PH 0.22±0.01e-g 0.20±0.00d 0.08±0.00f 0.08±0.00b
PR 0.23±0.00e 0.21±0.01d 0.08±0.00f 0.08±0.00b
PM 0.22±0.01fg 0.19±0.01d 0.07±0.00g-i 0.08±0.00b
Cycle 3
AH 0.30±0.01b-d 0.25±0.07c 0.12±0.00de 0.13±0.00a
AR 0.29±0.01cd 0.36±0.01b 0.12±0.00c-e 0.13±0.06a
AM 0.30±0.01a-c 0.36±0.01b 0.12±0.00cd 0.13±0.00a
PH 0.29±0.01cd 0.36±0.00b 0.12±0.00bc 0.13±0.00a
PR 0.31±0.01ab 0.40±0.01a 0.14±0.00a 0.13±0.00a
PM 0.29±0.01ab 0.34±0.00b 0.12±0.00e 0.13±0.00a
Cycle 4
AH 0.30±0.01ab 0.35±0.01b 0.12±0.00c-e 0.13±0.00a
AR 0.31±0.01a 0.36±0.00b 0.12±0.00c 0.13±0.00a
AM 0.31±0.00ab 0.36±0.01b 0.12±0.00bc 0.13±0.00a
PH 0.29±0.01b-d 0.37±0.00b 0.13±0.00b 0.13±0.01a
PR 0.31±0.00a 0.41±0.01a 0.14±0.00a 0.13±0.00a
PM 0.29±0.01d 0.35±0.01b 0.12±0.00c-e 0.13±0.00a
Values are means of three replicates. Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly Prepared, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.
{ label needed for table-wrap[@id='t6'] }
Table 6 The stability of viscosity in selected soups as affected by freeze-thaw cycles (Pa·s)
Sample Ogbono Ewedu Okro (Ila) Kuka
Cycle 0
FP 2.00±0.00a 1.40±0.00a 1.80±0.00a 0.90±0.00a
Cycle 1
AH 1.99±0.00cd 1.39±0.00c 1.80±0.00a 0.89±0.00c
AR 1.96±0.00l 1.38±0.00ef 1.76±0.01ef 0.88±0.01gh
AM 1.98±0.00gh 1.38±0.00f 1.78±0.01c 0.89±0.00d
PH 1.99±0.00b 1.39±0.00de 1.78±0.01bc 0.90±0.00b
PR 1.98±0.00gh 1.39±0.00d 1.79±0.01b 0.88±0.00e
PM 2.00±0.01b 1.40±0.00ab 1.80±0.00a 0.89±0.00c
Cycle 2
AH 1.98±0.00h 1.38±0.00ef 1.79±0.01b 0.88±0.00e
AR 1.92±0.00o 1.37±0.01gh 1.73±0.00h 0.86±0.00k
AM 1.97±0.00k 1.36±0.00j 1.76±0.00ef 0.88±0.00g
PH 1.99±0.00de 1.37±0.00h 1.77±0.00d 0.89±0.00c
PR 1.97±0.00k 1.38±0.00g 1.77±0.01de 0.87±0.00i
PM 1.99±0.00c 1.40±0.00b 1.78±0.00b 0.89±0.00d
Cycle 3
AH 1.97±0.00d 1.37±0.00gh 1.79±0.00b 0.88±0.00g
AR 1.89±0.00p 1.35±0.00k 1.69±0.00i 0.83±0.00m
AM 1.95±0.00m 1.33±0.00m 1.75±0.00g 0.87±0.00j
PH 1.98±0.00fg 1.36±0.00j 1.76±0.01ef 0.89±0.00d
PR 1.95±0.00m 1.37±0.00i 1.76±0.01f 0.85±0.00l
PM 1.99±0.00k 1.40±0.00bc 1.79±0.00b 0.88±0.00f
Cycle 4
AH 1.97±0.00k 1.36±0.00i 1.78±0.00bc 0.87±0.00ij
AR 1.85±0.00q 1.33±0.00n 1.65±0.01j 0.81±0.00n
AM 1.94±0.00n 1.31±0.00o 1.73±0.00h 0.85±0.00kl
PH 1.98±0.00i 1.34±0.00l 1.76±0.00f 0.88±0.00e
PR 1.93±0.00n 1.35±0.00j 1.74±0.00g 0.84±0.00m
PM 1.99±0.00f 1.39±0.00bc 1.78±0.01bc 0.87±0.00h
Values are means of three replicates. Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly Prepared, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.

Free fatty acid (FFA)

The soups` free fatty acid values varied from 0.56 ±0.01 to 3.09±0.32% (Table 2). Free fatty acid is formed due to the hydrolysis of triglycerides and is responsible for off flavor development during storage.

High temperature, moisture, and presence of active lipase are responsible for the production of FFA in fat containing food products (Kumar et al., 2009). Among the freshly prepared soups, ewedu had the least FFA value (0.56±0.01%). This suggested that ewedu might be more stable than others during storage. Further study revealed that the highest free fatty acid values were observed in soups packaged in both containers (plastics and aluminium) and thawed at ambient condition, while microwave thawed soups in plastic containers had the lowest FFA contents 
(Table 2). Variation in FFA values of the 
freeze-thawed soups indicated that the cycle significantly affected lipid hydrolysis. The increase in FFA was found markedly higher during the third freeze-thaw cycle of the 4-cycle experiment. This might be due to maximal lipase release from liposomes during the third freeze-thaw cycle (Sikorski and Kolakowski, 2000), making the enzyme close the substrate. Since the formation of FFA does not directly lead to nutritional losses, its assessment is deemed important when considering rancidity occurrence in food. However, the
pro-oxidant effect of FFA on lipid matter was based on the catalytic effect of thecarboxyl group on the development of free radicalsby the decomposition of hydro-peroxides (Yoshida et al., 1992). In addition, it has been established that interaction between FFA and proteins leads to texture deterioration (Mackie, 1993).

Peroxide value

The soups` peroxide values ranged from 5.82±0.22 to 14.54±0.25 mEq/kg (Table 3). The peroxide value (PV) which is a biochemical lipid oxidation index (peroxide value) was used o evaluate the development of rancidity in the soups subjected to freeze-thaw cycles. Lipid peroxidation products, especially aldehydes, cause rancidity and food deterioration (Undeland, 2001). It was observed that the peroxide value increased as the freeze-thaw cycle increased. However, the least PV at every
freeze-thaw cycle was observed in microwave thawed soups in plastic containers. The observed increase indicated that hydrolysis of lipids occurred during storage.

Egan et al. (1981) reported that acidity and a rancid taste were noticed in food when peroxide value was in the range of 20 to 40 mEq/kg. A moderate peroxide formation was detected during the frozen storage period, except for the end of the experiment when the highest mean values were obtained. This was similar to the findings of Akusu and Kiin-Kabari (2013) who reported on the effect of storage period on selected functional, chemical stability and sensory properties of bush mango (Irvingia gabonensis) seed flour. Room temperature thawed soups in plastic containers had the highest values at each cycle and the values obtained were approaching the unacceptable limits of 20 mEq/kg at the fourth cycle. This implies that the shelf life of room temperature thawed soups in plastic containers cannot be guaranteed beyond the fourth freeze- thawed cycle.

pH

The soups` pH values ranged from 6.53±0.06 to 7.17±0.06 (Table 4). It was observed that the pH decreased as the freeze-thaw cycle increased.This was due to the differences in the thawing methods as well as the packaging materials. The highest pH values reductions were obtained in room temperature thawed soups in plastic containers at every freeze-thaw cycle. Since pH is a measure of the amount of free hydrogen ions (H+) in a solution, denaturation of buffer proteins could be caused by freezing as a result of exudates production, which might lead to the release of hydrogen ions and a subsequent decrease in pH (Leygonie et al., 2012).

A further explanation for this finding might be due to microbial or enzymatic deamination of proteins that might result into the release of hydrogen atoms (Leygonie et al., 2011).

Slight decrease in the pH of the soups indicated that fermentation might likely occur in the future. The pH changes are in agreement with the findings of Sigurgisladottir et al. (2000) who reported on the effects of freezing and thawing on the microstructure and the texture of smoked Atlantic salmon, but contrary to the findings of Simeonidou et al. (1998) who researched on the quality assessment of seven Mediterranean fish species during storage on ice and Arannilewa et al. (2005) who reported on the effect of frozen period on the chemical, microbiological and sensory quality of frozen tilapia fish (Sarotherodun galiaenus). The changes in pH indicated a direct relationship with sensory and microbiological results, and reflected similar trends in other storage stability parameters (titratable acidity, peroxide value, free fatty acid and viscosity).

Titratable acidity

The soups` titratable acid values varied from 0.07±0.01 to 1.39±0.00% (Table 5). The highest values of titratable acidity were observed in room temperature thawed soups in plastic containers at every freeze-thaw cycle. An increase in the titratable acidity values paralleled with the decrease in the pH of the freeze-thawed soups, as significantly influenced by the thawing methods and types of packaging materials. This finding was in agreement with the observation of Adewusi (1999) who reported the effect of processing on total organic acids content and mineral availability of simulated cassava-vegetable diets.

Viscosity

Viscosity values of the soups ranged from 1.31±0.00 to 2.00±0.00 Pa·s (Table 6). The viscosity values obtained decreased as the freeze-thaw cycle increased. The lowest viscosity values reductions were obtained in microwave thawed soups in plastic containers at every freeze-thaw cycle. The values obtained in this study was in line with those reported by Akusu and Kiin-Kabari (2013) on ‘ogbono’ soups made from stored bush mango (Irvingia gabonensis) seed flour (0.88-1.35 Pa·s) and Eze and Akubor (2012) who did the research on the effect of drying methods and storage on the physicochemical properties of okra and observed that the viscosity of okra samples varied from 1.50-1.60 Pa·s, with the fresh sample having the highest value of viscosity. From the previous findings, it could be deduced that the rate of moisture loss corresponded with the decrease in the viscosity of all the samples at every freeze-thaw cycle. This was correspondence with the findings of Eze and Akubor (2012) who reported that the rheological and hydrophilic properties of starch and gums in food systems might be altered by heat.

Freezing and thawing effects on microbiological quality of soups samples

There was no evidence of fungal contamination on the soup samples analyzed and this might be due to cooking temperature (100 °C) that was able to eliminate the initial fungal population. Bacterial population was recorded in the samples subjected to plate count method. The bacterial counts obtained ranged from 1.50±0.17 to 2.92±0.02 Log CFU/mL (Table 7). However, the homogeneity of the bacteria present in the soups samples and the impact of thawing on the soups were assumed to be randomly distributed across the samples and were therefore not factored into the analysis. Freshly prepared okro (ila) and ogbono soups cooled down to room temperature had the highest bacterial counts 2.92±0.02 Log CFU/mL and 2.80±0.02 Log CFU/mL, respectively. Lower bacterial counts were recorded for freshly prepared ewedu and kuka soups (2.51±0.30 Log CFU/mL and 2.34±0.01 Log CFU/mL). The results obtained showed that all the soup samples had bacterial count of < 104 CFU/g (4.0 Log CFU/g). Some bacteria were suspected to be present in the soups. and the suspected bacteria were Bacillus cereus, Bacillus subtilis and Escherichia coli. It was observed that Bacillus spp were the dominant organisms in ogbono, ewedu and ila soups, while the major organism in ewedu soup was Escherichia coli (Tables 8 and 9{ label needed for table-wrap[@id='t9'] }). Most strains of Escherichia coli are harmless and opportunistic in nature (Rodríguez-Lozano et al., 2010). The presence of Escherichia coli in foods is not alwaysalarming because most strains are harmless and opportunistic in nature (Cohen et al., 2006). However, the bacterium is well known as an indicator of fecal contamination level during handling and processing (Sachey et al., 2001). Bacillus spp are sporulated and thermal resistant bacteria that are widely distributed in nature, and often associated with different food products. Spore formation confers to bacteria resistance to pasteurisation treatments (Rodríguez-Lozan et al., 2010).

Table 7 Bacterial examination of the freeze-thaw Nigerian soups
Samples Ogbono
(Log 10 CFU/mL)
Ewedu
(Log 10 CFU/mL)
Ila
(Log 10 CFU/mL)
Kuka
(Log 10 CFU/mL)
Cycle 0
FP 2.80±0.02 a 2.51±0.30a 2.89±0.06ab 2.34±0.01ab
Cycle 1
AH 2.79±0.01a 2.44±0.31b 2.88±0.02ab 2.31±0.0 a-d
AR 2.79±0.02a 2.37±0.30cd 2.92±0.02a 2.35±0.02 a
AM 2.75±0.02ab 2.35±0.30c-e 2.85±0.01b-e 2.29±0.01 a-e
PH 2.64±0.03 a-d 2.29±0.28d-f 2.82±0.01 c-f 2.26±0.01 b-f
PR 2.73±0.05 a-c 2.42±0.29bc 2.85±0.01 b-d 2.30±0.00 a-e
PM 2.58±0.03 c-f 2.20±0.28g 2.64±0.01 k 2.13±0.02 hi
Cycle 2
AH 2.73±0.02 a-c 2.31±0.27de 2.79±0.01fg 2.29±0.03 a-e
AR 2.79±0.01 a 2.34±0.29 de 2.86±0.02bc 2.33±0.02 a-c
AM 2.67±0.03 a-c 2.33±0.29 de 2.81±0.01e-g 2.25±0.03 c-g
PH 2.62±0.02 b-e 2.33±0.33de 2.81±0.02e-g 2.17±0.02 g-i
PR 2.70±0.00 a-c 2.36±0.29cd 2.81±0.02d-g 2.27±0.01a-e
PM 2.22±0.07gh 2.18±0.29gh 2.55±0.05 l 1.97±0.03j
Cycle 3
AH 2.67±0.03 a-c 2.28±0.27ef 2.74±0.04h-j 2.24±0.01 d-g
AR 2.65±0.08 a-c 2.32±0.28de 2.79±0.01fg 2.26±0.00 b-f
AM 2.71±0.02 a-c 2.32±0.31de 2.78±0.00 f-h 2.22±0.02e-g
PH 2.49±0.01d-f 2.36±0.32cd 2.73±0.01ij 2.10±0.02 i
PR 2.64±0.03 a-d 2.35±0.30c-e 2.80±0.03fg 2.22±0.03 e-g
PM 2.10±0.17 h 2.11±0.38hi 2.56±0.03 l 1.82±0.07 k
Cycle 4
AH 2.45±0.08 f 2.23±0.28fg 2.74±0.01h-j 2.19±0.03 f-k
AR 2.58±0.03 c-f 2.30±0.27 d-f 2.77±0.01g-i 2.24±0.03 d-g
AM 2.48±0.00 e-f 2.30±0.30 d-f 2.77±0.01f-i 2.17±0.02 g-i
PH 2.25±0.13 g 2.28±0.39ef 2.71±0.01j 1.94±0.06 j
PR 2.22±0.07gh 2.29±0.32 d-f 2.79±0.01fg 2.24±0.03 d-g
PM 1.83±0.30 h 2.08±0.53 i 2.54±0.05l 1.50±0.17 l
Values are means of three replicates. Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly Prepared, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.
Table 8 Biochemical reactions of isolated bacteria in freshly prepared soups
Samples Coagulase test Indole test Catalase test Oxidase test Gram staining test Suspected organisms
Ogbono 1 - + +         - Bacillus cereus
Ogbono 2 - + +         - Bacillus cereus
Ogbono 3 - + +         - Bacillus cereus
Ewedu 1 - + + -         - Escherichia coli
Ewedu 2 - + + -         - Escherichia coli
Ewedu 3 - + + -         - Escherichia coli
Ila 1 - + +         - Bacillus cereus
Ila 2 - - + -         - Bacillus subtilis
Ila 3 - - + -         - Bacillus subtilis
Kuka 1 - + +         - Bacillus cereus
Kuka 2 - + +         - Bacillus cereus
Kuka 3 - + +         - Bacillus cereus
(+) present; (-)absent
{ label needed for table-wrap[@id='t9'] }
Table 9 Biochemical reactions of isolated bacteria in freeze-thawed soups
Sample Coagulase test Indole test Catalase test Oxidase test Gram staining test Suspected organisms
Ogbono
AH - + +         - Bacillus cereus
AR - + +         - Bacillus cereus
AM - + +         - Bacillus cereus
PH - + +         - Bacillus cereus
PR - + +         - Bacillus cereus
PM - + +         - Bacillus cereus
Ewedu
AH - + + -         - Escherichia coli
AR - + + -         - Escherichia coli
AM - + + -         - Escherichia coli
PH - + + -         - Escherichia coli
PR - + + -         - Escherichia coli
PM - + + -         - Escherichia coli
Ila
AH - - + -         - Bacillus subtilis
AR - - + -         - Bacillus subtilis
AM - + +         - Bacillus cereus
PH - + +         - Bacillus cereus
PR - + +         - Bacillus cereus
PM         - - + +         - Bacillus cereus
Kuka
AH - + +         - Bacillus cereus
AR - + +         - Bacillus cereus
AM - + +         - Bacillus cereus
PH - + +         - Bacillus cereus
PR - + +         - Bacillus cereus
PM         - - + +         - Bacillus cereus
PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature. (+) present; (-) absent

Ideally, the cooking temperature should be able to destroy all viable microorganisms, but the bacterial load recorded could be as a result of the presence of
thermo-resistant micro organisms (Gould, 2000) that were able to withstand the cooking temperature (100 °C). The viscosity of the soups or other ingredients from the soup recipes such as oil might protect the identified organisms against the lethal effect of the heat treatment 
(Rodríguez-Lozan et al., 2010). Bacillus enzymes are resistant to pasteurisation treatment (Barefoot and Adams, 1998; Rodríguez-Lozan et al., 2010) and are usually destroyed at sterilization temperature of 120 °C for 10-15 min (Gould, 2000; Pflug and Gould, 2000).

Freezing of the soups packaged in aluminum and plastic containers, followed by freezing and thawing using different thawing methods at 5 days interval up to 20 days frozen storage caused significant reduction in the number of bacterial counts when compared to freshly processed samples, regardless of thawing conditions and packaging materials. The methods of thawing frozen foods determine the rate at which microbial population would grow during and after thawing 
(Leygonie et al., 2012).The thawing methods employed in this study had significant influence on the microbial growth and these were presented in Figure 1.

Fig. 1 Destruction of bacterial cells in A -ogbono soups; B - ewedu soups; C - ila soups; D - kuka soups subjected to 
freeze-thawed cycles. No= Initial microbial population N= Final microbial population O= Freshly prepared Ogbono soup, PH= Packaged in plastics but thawed with hot water, AH= Packaged in aluminium but thawed with hot water, PM= Packaged in plastics but thawed with microwave AM= Packaged in aluminium but thawed with microwave, AR= Packaged in aluminium but thawed at room temperature and PR= Packaged in plastics but thawed at room temperature.
CJFST10-2-206-f1

The obtained microbial inactivation values varied from 0 to 42.0% of the initial population in okro (ila) soup samples, 0-44.40% of the initial population in ewedu soup samples,0-85.0% of the initial population in ogbono soup samples and 0-100.0% of the initial population in ewedu soup samples. This observation is consistent with the results presented by 
Georgsson et al. (2006) who described the fragility of the organisms relative to the freezing process. The repetitive mechanical freezing process or desiccation of the frozen product over the storage period might be responsible for the considerable reduction in the bacterial counts (Georgsson et al., 2006). The structural disarray caused by the freezing process might result into loss of fluid that is rich in proteins, vitamins and minerals (Leygonie et al., 2012), which consequently provides an excellent medium for microbial medium for microbial growth. The bacteria counts of < 104 CFU/g 
(4.0 Log CFU/g) indicated a tolerable level of contamination (FAO, 1979; Ossai, 2012) and this might not pose any health risk if the storage and handling practices are under strict hygienic control. Microwave thawed soups in plastic containers had high rate of microbial destruction when compared with other procedures. This happened because microwave heating is a rapid process and heat distribution during microwave heating is more uniform than conductive heating (Karel and Lund, 2003), which is less uniform, time consuming and encourages microbial build up (Leygonie et al., 2012).

Sensory qualities of freshly prepared and 
freeze-thawed selected soup

The results of sensory evaluation of re-frozen soups are presented in Tables 10-13{ label needed for table-wrap[@id='t11'] }{ label needed for table-wrap[@id='t12'] }{ label needed for table-wrap[@id='t13'] }. Statistical analysis of the freeze-thawed soups assessed for organoleptic characteristics (taste, colour, aroma, consistency and overall acceptability) revealed significant differences (p<0.05) in the organoleptic characters within the column (Tables 10-13{ label needed for table-wrap[@id='t11'] }{ label needed for table-wrap[@id='t12'] }{ label needed for table-wrap[@id='t13'] }). Freshly prepared soups were rated significantly (p<0.05) higher than others and they were the mostly preferred. Room temperature thawed soups in aluminium containers had the least scores for all the sensory attributes. Panelists rated microwave thawed soups in plastic containers significantly (p<0.05) higher than other freeze-thawed soups for taste, colour, aroma, consistency and overall acceptability.

Table 10 Sensory qualities of freshly prepared and freeze-thawed ogbono soups after 4thcycle
Sample Taste Colour Aroma Consistency Overall Acceptability
FP 8.50±0.69a 8.15±0.93a 8.10±0.97a 8.35±0.75a 8.25±0.79a
AH 5.45±0.83d 5.30±0.80d 5.15±0.93d 5.30±0.87d 5.20±0.83d
AR 3.45±0.89e 3.50±1.00e 3.45±1.10f 3.70±1.03e 3.80±1.10e
AM 5.65±0.81d 5.70±1.08d 5.55±1.10d 5.65±0.99d 5.65±0.67d
PH 6.40±0.75c 6.50±1.05c 6.05±0.61c 6.20±0.70c 6.35±0.59c
PR 3.60±0.75e 3.85±0.67e 4.15±0.75e 3.85±0.81e 4.20±0.77e
PM 7.20±0.83b 7.25±0.85b 7.50±0.83b 7.35±0.81b 7.55±0.61b
Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly prepared, PH= Packaged in plastics, thawed with hot water, AH= Packaged in aluminium, thawed with hot water, PM= Packaged in plastics, thawed with microwave AM= Packaged in aluminium, thawed with microwave, AR= Packaged in aluminium, thawed at room temperature and PR= Packaged in plastics, thawed at room temperature.
{ label needed for table-wrap[@id='t11'] }
Table 11 Sensory qualities of freshly prepared and freeze-thawed ewedu soups after 4th cycle
Sample Taste Colour Aroma Consistency Overall Acceptability
FP 8.45±0.69a 8.20±0.83a 8.05±0.95a 8.40±0.75a 8.25±0.79a
AH 5.55±0.89d 5.35±1.04d 5.10±0.91d 5.40±1.10d 5.20±0.83d
AR 3.50±0.95e 3.60±1.00e 3.40±1.10f 3.65±1.00e 3.80±1.11e
AM 5.75±0.85d 5.55±1.00d 5.45±1.10d 5.80±0.95cd 5.65±0.67d
PH 6.40±0.75c 6.45±1.00c 6.10±0.64c 6.30±0.66c 6.35±0.59c
PR 3.60±0.75e 3.90±0.72e 4.10±0.79e 3.85±0.67e 4.20±0.77e
PM 7.30±0.80b 7.30±0.73b 7.45±0.89b 7.65±0.59b 7.55±0.61b
Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly prepared, PH= Packaged in plastics, thawed with hot water,
AH= Packaged in aluminium, thawed with hot water, PM= Packaged in plastics, thawed with microwave AM= Packaged in aluminium, thawed with microwave, AR= Packaged in aluminium, thawed at room temperature and PR= Packaged in plastics, thawed at room temperature.
{ label needed for table-wrap[@id='t12'] }
Table 12 Sensory qualities of freshly prepared and freeze-thawed ila soups after 4th cycle
Sample Taste Colour Aroma Consistency Overall Acceptability
FP 8.45±0.69a 8.00±0.97a 8.05±0.95a 8.00±0.92a 8.20±0.83a
AH 5.55±0.89d 5.25±0.97d 5.10±0.91d 5.12±0.75d 5.20±0.83d
AR 3.50±0.95e 3.65±1.04e 3.40±1.10f 3.45±1.00e 3.85±1.09e
AM 5.75±0.85d 5.30±1.03d 5.45±1.10d 5.40±0.75d 5.60±0.68d
PH 6.40±0.75c 6.40±0.94c 6.10±0.64c 6.35±0.67c 6.45±0.61c
PR 3.60±0.75e 3.90±0.72e 4.10±0.79e 3.80±0.77e 4.25±0.85e
PM 7.30±0.80b 7.35±0.81b 7.45±0.89b 7.40±0.75b 7.50±0.61b
Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly prepared, PH= Packaged in plastics, thawed with hot water,
AH= Packaged in aluminium, thawed with hot water, PM= Packaged in plastics, thawed with microwave AM= Packaged in aluminium, thawed with microwave, AR= Packaged in aluminium, thawed at room temperature and PR= Packaged in plastics, thawed at room temperature.
{ label needed for table-wrap[@id='t13'] }
Table 13 Sensory qualities of freshly prepared and freeze-thawed kuka soups after 4th cycle
Sample Taste Colour Aroma Consistency Overall Acceptability
K 8.35±0.81a 8.45±0.61a 8.15±0.88a 8.10±0.85a 8.00±0.86a
AH 5.20±0.77d 5.30±1.17c 5.15±0.99d 5.20±0.83d 5.30±0.57c
AR 3.35±0.88e 3.35±0.81d 3.60±1.05e 3.65±1.18e 3.80±1.11e
AM 5.50±0.83d 5.50±0.95c 5.40±0.94d 5.40±0.75d 5.55±0.51c
PH 6.50±0.83c 6.60±1.00b 6.05±0.76c 6.35±0.81c 6.25±0.55b
PR 3.55±0.76e 3.85±0.67d 4.15±0.81e 4.15±0.88e 4.45±0.69d
PM 7.45±0.83b 7.10±0.64b 7.30±0.80b 7.40±0.68b 7.65±0.59a
Mean values having different superscripts within a column are significantly different (p<0.05). FP = Freshly prepared, PH= Packaged in plastics, thawed with hot water,
AH= Packaged in aluminium, thawed with hot water, PM= Packaged in plastics, thawed with microwave AM= Packaged in aluminium, thawed with microwave, AR= Packaged in aluminium, thawed at room temperature and PR= Packaged in plastics, thawed at room temperature.

The nature of the packaging materials and thawing conditions hada significant influence on the organoleptic characteristics of the soups. This is similar to the findings of Goral (2008) who reported the effect of different techniques of freezing and defrosting on the quality of spice vegetables after a long-term frozen storage. Plastic containers absorbed heat and retained it to thaw the soups packed in them at a considerable rate in hot water and microwave thawing conditions, while aluminum containers conducted heat away from the soups they contained, creating less effective thawing rate in hot water and microwave thawing conditions (Raji et al., 2016). The slowest rate of defrosting was obtained in soups packaged in aluminium containers and thawed under atmospheric condition. In addition, the reductions in the organoleptic attributes might be due to activities of spoilage agents (Oriakpono et al., 2011) and biochemical changes occurring therein with increasing thawing time (Alizadeh et al., 2007).

Conclusions

The results of this research revealed that deterioration of the soups increased as the number of freeze-thaw cycle increased. Both types of packaging materials as well as methods of thawing, besides the number
freeze-thaw cycles, had a significant influence on the stability and sensory quality of the soups. Microwave-thawed plastic packed soups had limited deteriorative changes and the highest rate of microbial inactivation at each cycle when compared with other thawing methods. In addition, microwave-thawed plastic packed soups were mostly preferred by panelists. However, their stability cannot be guaranteed if the cycle is above three, because of deteriorative increase in free fatty acid and peroxide values.

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