MATERIALS AND METHODS

Studies on the effect of storage period on the chemical composition, pH and the coliform bacteria population of Wara cheese were carried out during the dry season (Jan/Feb) in the Microbiology laboratory of the Department of Animal Science, University of Ibadan. Nigeria. 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 in whey at room temperature and subsequent chemical and microbiological analysis carried out at the 15th, 39th, 63rd and 87th h of 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, while protein was determined by the micro Kjedahl method. Moisture and ash contents were determined by standard methods (AOAC, 1980). Results were statistically evaluated by analysis of variance (Steel and Torrie, 1980) while differences among means were detected using Duncan’s multiple range test (Duncan, 1955).

RESULTS AND DISCUSSION

Fresh Wara cheese contained 70.75% moisture, 39.00% fat, 37.08% protein and 2.53% ash while pH and cbc were 4.85 and 472.75*10⁵ cfu g^-1 (Table 1). These results except for %ash content, which was lower, falls within the range of previous findings (Fashakin and Unokiwedi, 1992; Ogundiwin and Oke, 1983; Belewu, 2001). Absence of standard processing methods explains the variations observed in the nutrient composition of cheese in developing countries (Turkoglu et al., 2003; Belewu, 2001). The effect of storage period on the moisture content was significant (p<0.01). The average moisture content on days 0, 1, 2 and 3 were 70.75, 71.50, 81.75 and 76.00%, respectively and averaged 75.00% for the whole storage period. As the pH of curd and whey decreases prior to draining, more calcium is transferred from the curd into the whey. Generally, this transfer has been reported to effect an increase in cheese moisture content resulting in softer cheese. Contrariwise, the effects of storage period on the % fat and % protein contents were negligible. However, a consistent increase in the protein content of Wara cheese was observed during storage.

Table 1:	Effect of storage period on the chemical composition and coliform count of Wara cheese
abc: Means in the same column differently superscripted differ significantly (p<0.05)

Table 2:	Correlation analysis of parameters observed during storage
*: p<0.05

Fig. 1:	The effect of storage period on the chemical composition and coliform count of Wara

The mean values were 37.08, 36.96, 37.64 and 41.10% on 0, 1, 2 and 3 day of storage. The increase observed in the protein content might probably be partly of bacterial origin, important in this respect is the lactic acid bacteria which have been reported to be the most predominant in fermented milk products by low pH (Gomez et al., 1989). In addition, a progressive increase in the total content of free amino acids has been reported during ripening of Mahon cheese (Garcia-Palmer et al., 1997). Proteolysis in cheese has been shown to directly affect the development of the desired aroma, texture and intensity of background flavour of most mature ripened cheese (Engels and Viser, 1994; Fox, 1989).

Most thermal processing has been found to leave heat-stable lipolytic enzymes almost intact thereby influencing food quality (Deeth and Fitz-Gerald, 1976). In this study, the 0.8% unit increase in %fat content up till the second day of storage was lower than the 1.07% unit decrease between the second and third day of storage. This result parallel previous findings (ABD EL-Salam et al., 1978) in which storage period had a significantly (p<0.01) positive effect on the fat content of the Egyptian Ras cheese. The % ash contents of Wara cheese were similar during storage except for day 2, which was significantly higher (2.99%). pH tends to decrease with storage period. The increasing acidity in stored Wara cheese would probably increase its shelf life by inhibiting the growth of spoilage and pathogenic microorganisms thus making it safer for human consumption (Fig. 1). A highly significant (p<0.01) correlation (r = 0.604) was found between pH and % ash content of Wara (Table 2). In addition, the correlation between pH and the % fat content of Wara cheese was negative (r = -0.554; p<0.01). Coliform bacteria count was significantly (p<0.01) affected by storage period. The initial value was significantly higher than the declining values during storage (Table 1). This observation corroborates previous findings in which maximum coliform counts were found in the curd, whilst minimum values occurred at the storage periods (Gomez et al., 1989; Mormur et al., 1994; Gaya et al., 1983). Earlier report also revealed inhibition of E. coli from the onset of fermentation and complete elimination after 24 h of storage (Feresu and Inyati, 1990). A significant though negative correlation (r = -0.60; p<0.05) was observed between cbc and the % moisture content. However, Turkoglu et al., (2003) in studies with Orgu cheese reported a positive correlation (r = 0.474). Apart from acid production by lactic acid bacteria, there is the likelihood that these microorganisms produce different types and quantities of inhibitory products such as antibiotics, volatile acids and hydrogen peroxide during fermentation. This observation therefore suggests that a three-day storage period is probably an effective way of ensuring a minimal content of coliform bacteria in Wara cheese.

CONCLUSIONS

From the results of the study, it could be concluded that Wara can be stored in whey at room temperature without adverse effect on the nutritive value and consumer health. However, it is essential that a standardized production process on industrial scale be developed and hygienic quality be improved.