Preparation and Properties of Probiotic Frozen Yoghurt Made With Sweet Potato and Pumpkin

Abstract

Low-fat frozen yoghurt was made by using commercial probiotic (Lactobacillus acidophilus, Streptococcus thermophilus & bifidobacteria) and traditional (Lactobacillus delbrueckii ssp. bulgaricus & Streptococcus thermophilus) starters; as well as; roasted red sweet potato and pumpkin for enhancing nutritional and functional values of this products. The preparing mixes and resulting frozen yoghurt stored at-20ºC for 8 weeks were evaluated for physicochemical, bacteriological and organoleptic properties. The results revealed that, there was significant differences (p<0.05) in all properties studied among the mixes and resulting frozen yoghurt. Frozen yoghurt mixes made with traditional yoghurt starter and sweet potato had higher specific gravity, weight per gallon, freezing point and apparent viscosity, but lower in pH values than the mixes made with probiotic starter. Also, resulting frozen yoghurt prepared with traditional starter and sweet potato had higher specific gravity, weight per gallon, freezing time, melting resistance and acetaldehyde content, but lower in overrun % and diacetyl content than that made with probiotic starter. Counts of Lb. delbrueckii ssp. bulgaricus, Str. thermophilus (traditional starter) and Lb. acidophilus were the most numerous in pumpkin frozen yoghurt, followed by sweet potato frozen yoghurt. On the other hand, sweet potato frozen yoghurt had higher Str. thermophilus & bifidobacteria (probiotic starter) counts, than the other treatments. However, frozen storage for 8 wk was slightly effected on the viable bacterial counts determined of different frozen yoghurt treatments, and bifidobacteria counts were still higher along the storage period than the recommended minimum levels. Also, frozen yoghurt manufactured with probiotic starter; especially with sweet potato; had the highest total organoleptic scores. Therefore, low-fat frozen yoghurt with improved nutritional and functional values, and also good organoleptic properties could be made by traditional yoghurt and probiotic starters; as well as roasted red sweet potato and pumpkin.

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