Title Preservation of Tshidzimba, a cereal-legume composite porridge, through fermentation, canning and drying

Abstract

Traditional African foods are often rich in nutrients and play an important role in increasing variety in diets of people in rural areas. Tshidzimba is popular amongst the Vhavenda of South Africa. It is made from maize samp, milled peanuts and salt. However, it has a very short shelf life when stored at ambient temperature. Canning, drying and fermentation of Tshidzimba were investigated to increase shelf-life. Factors investigated were microbiological quality, nutrient content (in terms of fat and protein content), levels of essential amino acids, water activity and sensory acceptability. Unpreserved Tshidzimba had very high total plate counts, yeasts and moulds after 3 days of storage at 25°C. Fermentation reduced the yeasts and moulds by 102 and total plate counts by 103 after 21 days of storage at 25°C from those of unpreserved Tshidzimba. Drying reduced the yeasts and moulds by 104 and total plate counts by 105 after 21 days of storage at 25°C. Anaerobic spore formers were not detected in canned Tshidzimba after 21 days of storage at 25°C. Drying reduced the fat content probably due to fat oxidation at the elevated drying temperature (50°C). However, in general the preservation methods had little effect on the general nutrient content of Tshidzimba. Tshidzimba protein showed low lysine value compared to the estimates of amino acid requirements for infants. For Tshidzimba to be a good source of nutrients for infants, fortification with a higher proportion of legume grains is recommended. Drying seemed to increase lysine (2.61 g/100 g protein) compared to that of unpreserved Tshidzimba (2.28 g/100 g protein), while canning reduced lysine (1.97 g/l00 g protein), probably due to its participation in Maillard reaction at the high canning temperature (116°C/70 min). Fermentation increased methionine content probably due to fermentative microorganisms, which are known to produce some amino acids while fermenting food products. Canning seemed to have reduced the methionine content possibly due to Maillard reaction. Consumer panellists indicated that of the preserved Tshidzimba, dried Tshidzimba had high acceptance compared to canned and fermented Tshidzimba. Some panellists disliked the sour taste of fermented Tshidzimba. Dried Tshidzimba was perceived to have a firmer texture compared to unpreserved Tshidzimba. Further research could help to determine the appropriate temperature/time combination that can least affect the texture of dried Tshidzimba.