A study of the fermentation process <, and microbiological characteristics of Amabere Amaruranu, a Kisii fermented milk product

Abstract

Abstract Amabere amaruranu is a popular traditionally fermented milk product from the Kisii community. Kenya. The objective of this study was to document the production process of amabere amaruranu. to determine and study the predominant microbial groups present and to identify and characterize the dominant lactic acid bacteria (LAB) and yeasts from samples obtained in the field as a basis for possible development of starter cultures. A survey was undertaken to study the traditional processing of the product among 27 traditional milk processors. Interviews were conducted using a structured questionnaire, key informant interviews and observation. Some key informants demonstrated the application of the indigenous technical knowledge to verify accuracy of the process documentation. A total of 16 samples of the traditionally fermented milk product were obtained from several families in Kisii for laboratory analysis. The pl-l of the field samples was determined. as well as enumeration and isolation of the predominant micro-organisms. The total viable microorganisms, LAB, yeasts and moulds, and Enterobacteriaceae, were enumerated. Preidentification tests for LAB was preformed according to the morphological characteristics. namely catalase test, Gram stain, growth at 15°C and 45 °C, CO2 production from glucose and arginine hydrolysis. Amongst the LAB strains, 90 % were phenotypically identified using APT 50 CH. Yeast strains were identified using phenotypic methods and API 20C AUX. Two LAB isolates and one yeast isolate that were previously isolated from samples of amabere amaruranu were tested 111 different combinations for their ability to ferment fresh milk. The production process of amabere amaruranu involved the addition of milk into a previous batch product. Fresh milk was sieved arrd boiled, held at boiling point for 10-15 minutes; cooled for 10-20 minutes and then inoculated into the fermentation vessel and fermented at ambient temperature ranging from 18 °C-32 "C. The product was lumpy in nature and was more preferred when it had developed appreciable acidity, Two types of fermentation vessels were used; gourd (ekerandi) and plastic containers. The average total viable counts (TVC') of the milk samples were 8.06 logloch.l/ml for ekerandi and 8.24 logj.cfu/ml for the plastic containers. The average presumptive lactobacilli counts were 8.08 logrscfu/rnl for ekerandi and 7.26 logu.cfu/ml for the plastic containers while the presumptive lactococci were 7.85 log IOC fu/rn I and 7.12 logll,cfuirnl for ekcrandi and plastic containers, respectively. The yeasts and moulds counts averaged 4.65 loglOcfu/ml for ekerandi ~U1d6.07 loglocfu/ml for the plastic container samples. The average counts for Enterobacteriaceae were below 1.00 loglocfu/ml in ekerandi while their numbers were 2.17 logloc1'u/ml in milk samples Irom the plastic containers. The mean pl-I of the 16 samples that were obtained from the field ranged from 3.65 ±(),67 to 4.7 ±0.55, with an average of 4.()O ±O.93, for all the samples. Predominant LAB species were identified as Streptococcus thermophilus (25 <)/0), Leuconostoc inesenteroides (20 %) and Lactobacillus bulgaricus (15 %). Predominant yeast species were identified as Saccharomyces cerevisiae (25 %), Trichosporum mucoides (15 %), Candida famara (10 %) and Candida albicans (lO Two LAB isolates: Streptococcus thertnophilus and Leuconostoc mesenteroides, and one yeast isolate, Saccharomyces cerevisiae were investigated in different combinations for their ability to ferment fresh mille The starter cultures tested were effective in fermenting the milk as indicated by a drop in the pH of the milk from 6.44 :JO.OO to a range of 4.23+0.21- 4.42 ::!:0.17 and increase in titratabJe acidity from 0.06 J:O.OO to a range of 0.78 %:J:0.30-1.12 <),~) :l:1.00 during the fermentation period. Industrially important species such as Streptococcus thermophilus and Saccharomyces cerevisiae were isolated from the fermented milk. There is the need to identify these organisms using modern molecular methods and characterize the techno logical properties of the dominant types to facilitate selection and development of starter cultures from them for the production of amabere amaruranu.