Characteristics and Chemical Compositions of Rice Milk Kefir and Process Optimization to Obtain High Antioxidant Kefir

Abstract

Kefir is fermented using different kinds of milk and consumed to boost health benefits. Kefir cultures from Kamphaeng Phet and Nonthaburi Provinces in Thailand were fermented with rice milk and cow milk. The rice cultivars used were white rice (Khao Hom Mali 105), red rice (Khao Dang) and black rice (Khao Nin) collected from Kalasin Province, Thailand. Characteristics and chemical compounds present in Thai rice milk and cow milk kefir were studied. Results indicated that pH ranged between 4.5 and 6 with viscosity ranging between 1.5 and 7 cps. The ultrasonication method was effective for extraction of volatile compounds and determination of antioxidant activities. Rice milk kefir significantly (p<0.05) exhibited higher antioxidant activity than cow milk kefir. DPPH scavenging was recorded between 55% and 89%, while FRAP assay results were between 2.5 and 3 µg FeSO4/ml and total phenolic content ranged 0.1 to 0.6 mg GAE/ml.

Microbial analysis showed the presence of acetic acid bacteria and lactic acid bacteria in both rice milk and cow milk kefir from Nonthaburi Province but yeast was absent. No lactic acid bacteria and yeast were recorded in rice milk and cow milk kefir from Kamphaeng Phet Province. GC-MS analyses showed that amino acids and alcohols were found in variable amounts in both rice milk and cow milk kefir from Kamphaeng Phet and Nonthaburi Provinces, with ethanol and acetic acid found in almost all types of rice milk kefir. Our optimization study revealed that inoculation percentage and incubation temperature modified phenolic contents and acetic acid bacteria population as shown by the response surface model. Optimal conditions were incubation temperature at 27.5 °C and inoculation percentage of 4% v/v. High antioxidant kefir can be considered as a food additive as it contains probiotics or as a cosmetic ingredient.

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