Effects of Storage Conditions on Organic Acids Content and Sensory Properties of Cottage Cheese

Abstract

In order to conserve milk proteins and extend its shelf life, production of different cheeses is essential. Cottage cheese is grouped under soft cheeses. Soft cheeses are those cheeses that do not undergo maturation and are characterized with high moisture contents, low fats and mild pH. This characteristic increases their chances of microbial contamination which results in off- odors, discoloration and slime formation thereby shortening their shelf life. The objective of the present study was to evaluate acceptance of cottage cheese and effects of its quality changes as result of different storage conditions thereby improving its shelf life. Cottage cheese was prepared by collecting fresh pasteurized milk from a local processing joint (Fresha Diaries) located in Githunguri area (Kenya). In the laboratory the pH of the milk was determined then boiled. Vinegar was added resulting in curd formation. The curd was then heated to drain whey, cut, collected and stored inside polyvinylchloride mould, kept at room temperature 25 ̊C. Samples of cottage cheese were separated into 8 lots, each of which contained 25 samples which were packed under different conditions as follows; Fresh cottage sample (FR) (control sample) under normal conditions, Open sample (OP) under room conditions, Vacuum sample (V) under normal conditions, Frozen sample (F) at ̵18 ̊C, Refrigerated sample (Ref) at 4 ̊C, 10% honey sample (HON 1) at room temperature, 20% honey sample (HON 2) at room temperature, and 30% honey sample (HON 3) at room temperature. The samples were analyzed using High performance liquid chromatography (HPLC) method daily in the first week and once in subsequent weeks for a period of nine weeks. A standard HPLC methodology was developed and chromatographic conditions optimized with an isocratic elution done using 0.05N H2SO4 as mobile phase at a flow rate of 1mL/min and a column temperature of 60 ̊C at Coffee Research Foundation Ruiru. Basing on retention time of the organic acid standard, it was observed that there were a number of organic acid present in cottage cheese in the range of lactic acid> citric acid >Malic acid >Oxalic acid >Acetic acid. Levels of organic acid depended on storage conditions which in turn led to changes in organoleptic properties of cheese. A nine-point hedonic scale was used to evaluate the attributes for consumer’s acceptance varying from liked extremely (9) to dislike extremely (1). The sensory attributes evaluated were color, appearance, taste flavor, smell/odor and texture/mouth feel. Tests were applied to cheese stored under different conditions of 1 week and 4 weeks. The tests were carried out in individual sensory evaluation scores during 30 days of storage. The results showed that the first week received highest scores. However sensorial was not significant during storage of deep freeze and Vacuum (p>0.005) but the difference in sensory of cheese stored in normal fridge, 10% honey, 20% honey and 30% honey were significantly difference (p<0.005). Despite its nutrition values it is evident that cottage cheese has a small shelf life hence the shelf life can be improved by employing a combination of different physical conditions (Hurdle technology) most probably according to our study modified vacuum packaging and use of honey.