Determinination of the lactic acid bacteria (LAB) and yeasts associated with the traditional fermented camel milk product

Abstract

The purpose of the study was to determine the lactic acid bacteria (LAB) and yeasts associated with the traditional fermented camel milk product (suusac) of the Somali community in Kenya. The traditional method of suusac production was studied by use of questionnaire and documented. The microbial content profile and changes during fermentation were then determined. From 15 samples of traditionally fermented suusac, 45 LAB and 30 yeast strains were isolated and identified using API 50 CHL and API 20C AUX identification systems, respectively. The total viable microorganisms, LAB, coliforms, and yeasts and molds were enumerated. The isolates were investigated for their functional roles in the fermentation process, namely, acidification, flavour/aroma production and proteolytic activity. Fermentation trials with single and mixed strain cultures were investigated to assess their acidification and flavour-producing properties. The traditional production of suusac involves spontaneous fermentation of camel milk in smoked gourds at ambient temperature for 1-2 days. The milk is not subjected to heat treatment prior to fermentation. The isolated LAB species were identified as Lactobacillus curvatus (8% of total isolates), Lactobacillus plantarum (16%), Lactobacillus salivarius (8%), Lactococcus raffinolactis (4%) and Leuconostoc mesenteroides subsp. mesenteroides (24%). The isolated yeasts were Candida krusei (20%), Geotrichum penicillatum (12%) and Rhodotorula mucilaginosa (8%). In traditional suusac, LAB counts averaged 6.77 logiocfu/ml, while yeast counts were relatively lower (2.05 logiocfu/ml). Low coliform numbers were encountered (<1 logiocfu/ml). ♦ x UNIVERSITY Of NAIROBI The LAB produced considerable acidity and majority (60%) were homofermentative. The primary functional role of the LAB was fermentation of lactose to lactic acid, resulting in acidity levels ranging from 0.46-0.67% lactic acid equivalent. All the LAB isolates recorded high proteolytic activity, except for L. raffinolactis, which did not exhibit any proteolytic activity. The LAB showed varying degrees of diacetyl production. Of the LAB, L. curvatus recorded the highest diacetyl flavour score, corresponding to >30 mg diacetyl/ 100 ml of milk. The yeast isolates showed limited carbohydrate-assimilating capabilities, but played a role in flavour development and proteolysis. G. penicillatum produced diacetyl (3.1-10 mg/100 ml), although it did not exhibit any proteolytic activity. C. krusei exhibited some proteolytic activity, although its diacetyl-producing capacity in camel milk was minimal (0.5-3 mg/100 ml). C. krusei also played a role in mixed starter fermentation of camel milk by increasing the activity of the LAB cultures and improving product flavour. The use of C. krusei + L. plantarum (1:1) and C. krusei + L. curvatus (1:1) reduced the fermentation time by half as compared to the use of the cultures individually.