Influences of oxidation-reduction potential on kefir: Microbial counts, organic acids, volatile compounds and sensory properties

Abstract

The effects of oxidation-reduction (redox) potential (Eh) on microbiological and sensory characteristics, volatile compounds, and organic acids of kefir produced using wild or commercial culture were investigated during 21 d of storage. The Eh of the milk was modified using reducing or oxidizing chemical agents. Eh7 (Eh expresses at pH 7) values of control, reduced and oxidized kefirs produced using the wild kefir culture were −195.5, −206.1 and + 178.3 mV, while control, reduced and oxidized kefirs produced using the commercial kefir culture had Eh7 values of −199.6, −208.1 and + 180.7 mV, respectively, on 1 d of storage. Generally, the viability of microorganisms in the kefirs was adversely affected by oxidized conditions, but it was species- and strain-dependent. The Eh caused the change of metabolic routes of the microorganisms and, thereby, the change of volatile compounds and organic acids contents of kefir. Principal component analysis (PCA) of the volatile compounds separated the kefirs according to the culture and redox status. Kefirs with low Eh were characterized by the presence of sulphur compounds, whereas kefirs with oxidative Eh were characterized mainly by aldehydes and diacetyl. In addition, reduced Eh caused arising in sensory preference of the kefir samples.