A study of making concentrated starter culture for Mala production in Kenya with special emphasis on small scale manufacturers

Abstract

The overall objective of this study was to produce a bulk concentrated mala culture for use directly producers. culturing composed in mala production by small scale mala 'Mala' is a sour milk product obtained by pausterised milk with a liquid culture of Streptococcus cremoris, S. diacetilactis and Leuconostoc citrovorullJ.It is an improved version of a Kenyan traditional sourmilk product called 'maziwa lala'. The concentrated mala culture should keep well under available preservation conditions in order to give the small scale manufacturers with adequate stocks to last them a convenient time period before replenishing. The growth of the culture was investigated in three media, namely skimmilk, whey and tryptone, both when buffered with calcium carbonate or not, It was then harvested by centrifugation and resuspended in the concentrated form in 10% sterile milk. The keeping quality of the concentrated culture was evaluated under frozen and freeze-dried conditions. Lactose, yeast extract, glycerol and glycerine were used as cryoprotective agents during the keeping quality studies. During the storage studies the culture was tested for its viability, species balance, activity and its functionality in mala production. It was found that the three media were equally good in supporting growth of the culture during preservation period. However, buffered whey was preferred because it is a by-product in cheesemaking and was more appropriate in terms of ease of centrifugation and cell yield. The cryoprotective agents improved the keeping quality of the deep frozen culture. Glycerol and Glycerine were however more effective and could help maintain the quality of the culture upto 4 months. Temperatures at -30°C were better than -20°C in this regard. The concentrated mala culture produced mala, of acceptable quality. Quantities of500g were sufficient to process upto 100 litres of milk into acceptable mala,compared to 3 litres of mala culture prepared conventionally. The processing of mala was accomplished by direct inoculation of 100litres of milk without subculturing or pre-incubation. Freeze drying of the culture lowered its viability and its ability to produce lactic acid. It also changed the species balance by lowering the proportion of S. d i acetylactics and L. citrovorum responsible for aroma production. Deep freezing also reduced the viability and acidulating property of the culture, as well as lowering the proportion of the S. diacetylactics and L. citrovorum but to a lesser extent. However, both freeze dried and deep frozen cultures managed to produce acceptable mala. It is concluded that mala culture can be concentrated and preserved under the conditions of this study. The most economical method would be to grow the mala culture in whey buffered with calcium carbonate, concentrate by centrifugation and preserve by deep freezing at -32°C using glycerine as the cryoprotective agent.