Development of value-added low-fat yoghurts using mixed-fruits, Cassava flour (Manihot esculenta L.), Cereal mixture and evaluation of their physicochemical, microbiological and sensory properties

Abstract

Value-added yoghurts are reported to have many health benefits on humans compared to normal yoghurts because consumption of value-added yoghurts are associated with many therapeutic and nutritional properties. Therefore, value-added yoghurts are becoming popular among a health conscious population in Sri Lanka. The objectives of the research were to develop different lowfat value-added yoghurts incorporated with mixed-fruit pulp, cassava flour, Cereal mixture and evaluation of their physicochemical, microbiological and sensory properties. Recipes for low-fat yoghurt consisted of gelatin (0.4%; w/w), milk powder (2.8%; w/w), sugar (9.7%; w/w), coloring (0.13%; w/w), flavors (0.1%; v/v), culture (2.6%; v/v) and skim milk (83.4%; w/w). Three different mixed-fruit yoghurt products were prepared with the addition of 12.71%, 12.61% and 12.52% (w/w) fruit pulp and another three Cassava flour incorporated yoghurt were prepared with the addition of 3.25%, 4% and 4.5% (w/w) cassava flour. Further, three cereal yoghurt products were prepared using 8%, 10% and 12% (w/w) Cereal mixture (com, soya, rice and green gram). Physicochemical properties of all the yoghurts such as titratable acidity and pH (AOAC, 2002) were determined during storage at 4°C for 20 days. Furthermore, microbiological and sensory properties of yoghurts were also determined and were compared with those of a commercial brand of yoghurt. Sensory properties were determined on a seven-point hedonic scale using 18 members of trained sensory panel. Sensory results were analyzed using Kruskal Wallis non-parametric ANOVA test with STATISTIX Computer software (Ver 2.0) for Windows.

Cassava yoghurt (4%; w/w), Cereal mixture yoghurt (10%; w/w) and mixed-fruit yoghurt (12.71%; w/w) were selected as the best yoghurts because of their significantly higher (P<0.05) sensory properties. Titratable acidity of cassava yoghurt increased gradually from 0.64% in the beginning to 0.78% at the 15 days of storage. Titratable acidity of cereal yoghurt increased gradually from 0.64% in the beginning to 1.23 % in the 15th day of storage while the titratable acidity of mixed fruit yoghurt increased gradually from 0.64% in the beginning to 1.23 % in the 15th day of storage. Yeast and mold populations in all the yoghurts were less than 103 CFU/ml and E. coli was not detected throughout the storage period. Shelf-life of all three yoghurts was approximately 15 days considering the changes in titratable acidity, microbiological and sensory properties. Therefore, it can be concluded that Cassava flour, Cereal mixture (com, soya, rice and green gram) and mixed-fruit pulp can be introduced to the yoghurt industry successfully in order to develop novel value-added low-fat yoghurts with improved sensory and nutritional properties.