The Effect of Short-term Frozen Storage on the Chemical Composition and Coliform Microflora of Wara Cheese Wara Cheese under Frozen Storage
The effect of short-term frozen (-20°C) storage on the chemical composition, pH and coliform bacterial count (cbc) of Wara cheese was investigated. Wara cheese at day old contained 31.00% total solids, 38.26% fat, 33.14% protein, 3.39% ash, 69.00% moisture, 376.50 * 105 cfu g-1 coliform bacteria and a pH of 5.04. At the end of 3 days of frozen storage, average total solids, fat, protein, moisture and ash were found, respectively, 33.25, 35.45, 36.63, 66.75 and 3.88%, while values for pH and cbc were 4.65 and 63.50 * 105 cfu g-1. Daily differences obtained in the parameters observed during frozen storage were similar except for the total solids content that was significantly different (p<0.01). A superior and highly significant correlation (r = 0.664, p<0.01) was found between pH and cbc, while cbc had a positive correlation (r = 0.366) with moisture content.
Cheese production is a household operation in many developing countries. Livestock farming in general and milk products in particular still play an important socio-economic role in many developing countries (FAO, 1990). Cheese provides a useful service in extending the shelf life of a valuable human foodstuff - milk. Absence of standard processing methods explains the variations observed in cheese physico-chemical characteristics (Turkoglu et al., 2003; Belewu, 2001). The general standard of hygiene applied to milk production in developing countries is poor and as a result, the quality of milk and milk products is poor (Aneja, 1989; IFST, 1997). Coliform organisms in cheese indicate poor sanitation and process control although their presence does not threaten public health, (Nielson, 1976).
Freezing of foods, though helps to preserve their shelf life, color, flavor andnutritive value (Kuo and Gunasekaran, 2003), it also bring about certain physical and organoleptic changes, which may or may not be desirable (Hall and Alcock, 1987). Commercially produced cheese are frozen and stored to decrease the rate of ripening and prolong shelf life during marketing (Fontecha et al., 1996). However, little information is available on the effect of freezing on cheese microflora (Bricker and Van Hekken, 2004). The Nigerian soft cheese Wara is produced locally and consumed fresh. There is therefore the need to evaluate the changes in the chemical and some microbiological properties of Wara cheese under frozen storage in search of means of extending its shelf life. This study was therefore carried out to evaluate the effect of frozen storage on the chemical composition, pH andthe coliform bacterial count of Wara cheese.
Materials and Methods
Studies on the effect of short-term frozen storage on the chemical composition, pH andthe coliform bacterial count of Wara cheese were carried out during the late dry season between January and February in the Dairy Microbiology Laboratory of the Department of Animal Science, University of Ibadan, Nigeria. The soft cheese samples used in this study were purchased from local sellers in Ibadan, Nigeria. Collections were in four batches and each batch served as a replicate of the experiment. Samples were kept without delay under frozen temperature (-20°C) and subsequent chemical and microbiological analysis were carried out at the 15th, 39th, 63rd and 87th h of frozen storage treatment.
Appropriate dilutions of homogenized samples (11 g in 99 mL of sterile distilled water) were incubated in Violet Red Bile Agar (VRBA) (Oxoid) for coliform bacterial counts. pH was measured directly on a Metrohm-Herisau (Metrohm Ltd., Herisau, Switzerland) pH meter. Fat was analyzed by the standard Gerber method, ash and moisture contents by standard methods (AOAC, 1980), while the protein content was determined by the micro Kjedahl method. Results were statistically evaluated by analysis of variance, while differences among means were detected using Duncans multiple range test.
Results and Discussion
The chemical composition, pH and coliform bacteria count of Wara cheese during
frozen storage are presented in Table 1 and Fig.
1. The initial concentrations of total solids, fat, protein and ash were
found, respectively, 31.00, 38.26, 33.14 and 3.39% while values for pH and cbc
were 5.04 and 376.50* 105 cfu g-1. The initial values
observed for the moisture, fat and protein content fall within the range reported
by Afolabi (1991), Ogundiwin and Oke, (1983) and Okomanyi, (1997). They reported
that Wara cheese contained between 60.00-76.60% moisture, 30.00-48.00% fat and
36.63-41.10% protein. However, the 3.69% ash observed in this present study
fall below the range (5.00-12.00%). Seasonal variations in the mineral content
of pasture consumed by dairy animals could be attributed to the differences
observed in the ash content of milk and milk products. The decline (38.26 to
35.45; p>0.05) observed in % fat might probably be attributed to sub-optimal
lipolytic activities of microorganisms inherent in Wara cheese. Loney and Bassette
(1970) had earlier reported an increase in fatty acid concentration during cheese
storage. This result suggests that consumers who prefer less fat in diet may
freeze Wara cheese for 3 days. On the other hand, the increase observed in the
protein content of Wara cheese could be of microbial origin as a result of microbial
proliferation most especially the lactic acid bacteria which has been reported
to be the most predominant in fermented milk products by low pH (Gomez et
Wara cheese under frozen storage was observed to significantly retain more
minerals than those kept in whey at room temperature. Average values were 3.69
and 2.83% (Alalade and Adeneye, 2006) for frozen and room temperature storage.
Initial pH value of 5.04 was in agreement with previously reported range of
4.0-6.8 (Mormur et al., 1994; Kalogridou-Vassiliadou et al., 1994;
Alalade and Adeneye, 2006). Wara is a slightly acidic milk product. The pH of
Wara kept under frozen storage tends to be inversely proportional to the storage
period. The increasing acidity in stored Wara would probably increase the shelf
life and make it safer for human consumption by preventing the growth of coliform
as well as pathogenic microorganisms. High levels of coliform bacteria have
been associated with cheese produced via traditional processing methods. An
average value of 229.06 * 105 cfu g-1 was observed during
frozen storage. This result corroborates the findings of Mormur et al.
(1994), Gomez et al. (1989) and Tzanetaki et al. (1987) who reported
that cheese contained 102-108 cfu g-1. The
wide variation in CBC was a probable reflection of the unhygienic and unstandardized
method of processing. CBC values declined by 83.13% (p>0.05) at the end of
the 3-day frozen temperature treatment. The decline observed was in agreement
with the findings of Gaya et al. (1983). Though CBC value declined (p>0.05)
in Wara cheese, storage in whey at room temperature significantly reduced coliform
count from 472.75 to 21.00 * 105 cfu g-1 over the same
period of storage (Alalade and Adeneye, 2006). However, earlier report by Bricker
and Van Hekken (2004) that bacteria demonstrated similar survival in frozen
citratehomogenate, citrate glycerol homogenate and chunk cheese thus suggesting
that components in cheese provide cryoprotection for microflora did not hold
for Wara cheese during frozen storage. A highly significant correlation (p<0.01,
r = 0.664) was found between pH and cbc (Table 2). Humphrey
et al. (1993) and Yeow-Lim et al. (1996) noted that acid sensitivity
of coliform bacteria was a function of the temperature of the medium.
|| The effect of short-term frozen storage on chemical composition,
pH and coliform bacterial count of Wara
|abc: Means on the same column differently superscripted
differ significantly (p<0.05)
|| Correlation analysis of parameters observed during storage
||Effect of frozen storage on the chemical composition and microbiological
property of the Nigerian soft cheese on day 0 to 3 (Mean±SEM; n =
From the results of this study, it could be concluded that frozen storage treatment has no adverse effect on the chemical composition of Wara cheese. Besides, frozen storage, by reducing the coliform bacteria count of Wara cheese could increase its shelf life and makes it safer for human consumption.
AOAC, 1980. Official Method of Analysis of Association of Official Analytical Chemist. 12th Edn., Association of Official Analytical Chemist, Washington DC.
Afolabi, O.G., 1991. Comparative yield and composition of soft cheese (wara) made from cow’s milk and extracts of different Calotropis procera plant parts. M.Sc. Thesis, University of Ibadan. Nigeria.
Alalade, O.A. and J.A. Adeneye, 2006. The effect of storage period on the chemical composition and coliform microflora of wara cheese. Int. J. Dairy. Sci., 1: 126-130.
CrossRef | Direct Link |
Aneja, R.P., 1989. World survey of traditional milk products in India and neighbouring countries including Hemalayan region. FAO, 1990 Manuscript.
Belewu, M.A., 2001. Nutritional and rheological evaluation of West African soft cheese made from plant coagulant (Calotropis procera) during storage. J. Food Technol. Africa, 6: 93-95.
Direct Link |
Bricker, A.L. and D.L.H. Van, 2004. Effect of short-term frozen storage on cheese microflora. Acs. Chem. Soc. 26th National Meeting. Abstract No. AGFD93. August 26, 2004.
FAO, 1990. The technology of traditional milk products in developing countries. FAO Animal Production and Health Paper, No. 85, FAO of the United Nations, Rome, Italy, pp: 1-318.
Fontecha, J., M. Kalal, J.A. Medina, C. Palaezi and M. Juarez, 1996. Effect of freezing and frozen storage on the microstructure and texture of ewe’s milk cheese. Zeitschrift Fur Lebensmittel Untersuchung Und Forschung, 203: 245-251.
Direct Link |
Gaya, P., M. Medina and M. Nonez, 1983. Accelerated decrease of eterobacteriaceae counts during ripening of new milk nanchego cheese by lactic acid inoculation. J. Food Prot., 46: 305-308.
Gomez, R., C. Pelaez and E. Torre, 1989. Microbiological study of semi-hard goat cheese (Majorero). Int. J. Food Sci. Technol., 24: 147-151.
Hall, L.P. and S.J. Alcock, 1987. Effect of microbial enzyme on the quality of frozen foods. Food Microbiol., 4: 209-219.
Humphrey, T.J., N.P. Richardson, R.M. Stetton and R.J. Radbury, 1993. Effect of temperature shift on acid and heat tolerance in Salmonella enteritidis phage type 4. Applied Environ. Microbiol., 59: 3120-3123.
PubMed | Direct Link |
Institute of Food Science and Technology UK., 1997. Food safety and cheese. Food Sci. Technol. Today, 11: 43-45.
Kalogridou-Vassiliadou, D., N. Tzanetakis and E. Litopoulou-Tzanetakis, 1994. Microbiological and phisico-chemical characteristics of Anthotyro, a Greek traditional whey cheese. Food Microbiol., 11: 15-19.
Kuo, M.I. and S. Gunasekaran, 2003. Effect of frozen storage on physical properties of pasta filata and nonpasta filata Mozzarella cheeses. J. Dairy Sci., 86: 1108-1117.
Direct Link |
Loney, B.J. and R. Bassette, 1968. Changes in FFA’s and lactones in sterile concentrated milk during storage. J. Dairy Sci., 54: 343-348.
Mormur, M., C. Carretero, R. Pla and B. Guamis, 1994. Microbiological changes during ripening of Cendrat del Montsec, a goat milk cheese. Food Microbiol., 11: 177-185.
CrossRef | ISI | Direct Link |
Nielson, V.H., 1976. More research needed on contamination by coliform bacteria. Am. Dairy Rev., 38: 50-50.
Okomanyi, O.A., 1997. Yield and composition of wara from raw, sour and fortified milk. M.Sc. Thesis, University of Ibadan, Nigeria.
Turkoglu, H., Z.G. Ceylan and K.S. Dayisoylu, 2003. The microbiology and chemical quality of orgu cheese produced in Turkey. Pak. J. Nutr., 2: 92-94.
Direct Link |
Tzanetakis, N., E. Litopoulou-Tzanetakis and K. Manolkidis, 1987. Microbiology of Kopanisti, a traditional Greek cheese. Food Microbiol., 4: 251-256.
Yeow-Lim, T., T.J. Raynor, K.R. Ellajosyulla and S.J. Knabel, 1996. Synergistic effect of high temperature and high pH on the destruction of Salmonella enteritidis and Escherichia coli. J. Food Prot., 59: 1023-1030.
Direct Link |