ASSESSMENT OF THE SENSORY PROPERTIES OF YOGHURT OBTAINED FROM BLENDS OF POWDERED MILK AND TIGERNUT JUICE

Abstract

Introduction Yoghurt is a fermented milk product which is obtained by fermentation of milk using a mixed culture of Streptococcus thermophilus and Lactobacillus bulgaricus. Consumption of products such as yoghurt containing viable probiotic organisms helps to lowers blood pressure, bad cholesterol and risk of colon cancer [1]. Yoghurt does not only supply good quality proteins, it is also an excellent source of calcium, phosphorus, potassium and contains significant quantities of vitamins. Tigernut juice (Cyperus esculentus) is a nutritious and refreshing natural drink, for the young and old alike. It is produced by wet milling of tigernut and subsequently filtering the resultant slurry to obtain the filtrate which is the juice [2]. Consumption of tigernut products, especially its juice, helps in preventing heart disease, activates blood circulation and assists in reducing the risk of colon cancer [3, 4]. Tiger-nut juice, with its inherent nutritional and therapeutic properties, could serve as additional source of nutrients if used as a replacement for water in yoghurt production. Therefore the objective of this study was to assess the sensory properties of yoghurt produced by replacing water with tigernut juice. Materials and Method Tigernut and powdered milk were purchased from Kure Market in Minna, Niger State. Tigernut juice was prepared using the method described by Ocheme et al.[5]. Tiger-nuts seeds were sorted, contaminants such as stones and unwholesome nuts were removed after which the nuts were washed and rinsed with distilled water then soaked overnight. They were crushed and the crushed nut was sieved using muslin cloth. The filtrate was used as a replacement for water in reconstituting powdered cow milk. The reconstitution ratios were: 300g of milk+700ml Tiger-nut juice; 300g of milk+500ml of water +200ml Tiger-nut juice; 300g of milk+400ml of water+ 300ml Tiger-nut juice; 300g of milk+300ml of water+400ml Tiger-nut juice and 300g of milk+200ml of water+500ml Tiger-nut juice respectively. After reconstitution, the mixtures were pasteurized at 75oC for 15minutes and then allowed to cool to 45oC. A commercial yoghurt was used to innoculate the samples (3% w/w) after which they were incubated at 37oC for 12h. At the end of fermentation, the samples were subjected to sensory evaluation by a panel of 20 judges who were familiar with yoghurt using a 9-point hedonic scale. The attributes evaluated were colour, aroma, taste, mouthfeel and overall acceptability. The data obtained were subjected to one-way ANOVA and the means were separated by Duncan’s Multiple Range Test using SPSS version 20. Results and Discussion The mean sensory scores of the samples are shown in Table 1. Commercial yoghurt had a significantly (p<0.05) higher score for aroma and overall acceptability than the other samples. The scores for taste and colour increased with increasing quantity of tigernut juice although the commercial sample and the sample without tigernut juice were ranked higher. Generally, all the samples were acceptable.