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Effect of nanopowdered eggshell on the characteristics of probiotic yogurt.

D. G. Kamel




Effect of nanopowdered eggshell on the characteristics of probiotic yogurt.
D. G. Kamel*. Dairy Science Department, Assiut University Assiut, Egypt.

Eggshell (ES) is a waste product of the food industry that could increase environmental pollution. ES is an alternative, cheap, and bioavailable source of dietary calcium (Ca) that can be utilized to fortify the Ca content of probiotic yogurt using nanotechnology. The calcium content of commercial yogurt is limited to 190.0 mg 100g−1. The objective of this study was to produce probiotic yogurt (5.0—7.0 log cfu g−1) with high Ca content by fortification with nano-sized (0.02, 0.04, and 0.06 mg mL−1) ES powder (ESP). Nano-sized ESP was prepared by milling pre-boiled dried ES using mortar grinder Fritsch Pulverisette 2. The size of the milled powder was measured using PW 1700 X-ray diffractometer to ensure that the diameter of the nano-sized is 25 � 1.7 nm. Yogurt was manufactured by dividing the pasteurized milk into 4 aliquots portions to make the yogurt. The first portion (T1), second (T2), third (T3), and fourth (T4) portions were inoculated with 1% Lactobacillus delbruckii subsp. bulgaricus (Lb), 1% Streptococcus thermophilus (St), and 15% Bifidobacterium bifidum (Bb). T1 was considered as control while 0.02, 0.04, and 0.06 mg mL−1 of nano-sized ESP were added to T2, T3, and T4, respectively. All treatments were inoculated at 40�C until a pH of 4.6 was reached. Subsequently, the yogurt was cooled and stored at 4�C for 16 d. The acidity, Ca, sensory properties, Bb count, total bacterial count (TBC), yeast and mold counts were examined. This experiment was repeated 3 times using 3 different batches of raw milk. The addition of nano-sized ESP decreased acid development significantly (P < 0.05). The TBC significantly decreased (P < 0.05) to 6.1 log cfu g−1 as the concentration of nano-sized ESP increased to 0.06 mg mL−1. The addition of 0.06 mg mL−1 nano-sized ESP produced a high Ca (705.4 mg 100g−1) yogurt with an acceptable composition and quality as compared with control (197.6 mg 100g−1). All sensory evaluation showed that the addition of nano-sized ESP improved taste, appearance, body and texture of probiotic yogurt. Moreover, the addition of nano-sized ESP increased the shelf-life of probiotic yogurt as compared with control. The impact of nano-sized ESP in probiotic yogurt during storage on the nutritional benefits will be evaluated in subsequent studies.

Keywords: nanopowdered eggshell, functional yogurt, shelf life.