Teff and maize starches-lipid complexes as fat replacers in a low calorie Mozzarella imitation cheese

Abstract

Consumer awareness of diseases such as cardiovascular disease has driven policies to reduce amounts of fat in the diet. Food manufacturers have met this demand and there has been increased production of low fat and fat free foods. Fat replacers have been developed to meet the consumers demand but as fat is reduced there is a loss in functionality. This study investigated the effect of teff and commercial maize starch modified with monoglyceride, as a fat replacer on the rheological, microbiological, micro-structural and physico-chemical properties of an imitation Mozzarella cheese. Yeast and mould, Lactic Acid Bacteria and aerobic plate counts showed microbial activity in the imitation cheeses. These microbes could have contributed to the softening of the imitation cheeses during storage. At an increased concentration of 3% monoglyceride the LAB counts were significantly decreased due to possible antimicrobial activity of monoglyceride. The pH, water activity and moisture content of the imitation cheeses were comparable to the literature and did not change significantly during the study. Modified (1.5 and 3% monoglyceride) and unmodified starch (teff and maize) pastes (15% w/v of starch in water) were prepared in the autoclave and homogenised before addition to imitation Mozzarella cheeses to reduce the fat by 50%. The compressive firmness of the full fat imitation cheese was significantly higher than all the low-calorie cheeses. The addition of modified starches as a fat replacer decreased the firmness of the cheeses as compared to the full fat imitation cheese. This could be because addition of lipids to starches reduced the rigidity of starch gels which were added to the cheeses and also decreased syneresis and retrogradation due to the formation of amylose-lipid complexes. The rheometer was used to determine the softening point of the imitation cheeses. Addition of starch modified with monoglyceride at both 1.5 and 3% were found to significantly decrease the softening points of the imitation cheeses. This can be due to less hydrogen bonding of starch with water due to interaction of the monoglyceride with starch, increases the availability of free water to plasticise the cheese matrix which would lead to lower softening points. A modified Schreiber test was used to determine the meltability of the imitation Mozzarella cheese. The spread area and maximum diameter of the full fat imitation cheese was significantly greater than that of the low-calorie maize imitation cheese throughout storage. Imitation cheeses containing modified and unmodified teff had significantly greater meltability in terms of spread area and diameter than maize starch initially, but later in storage the cheeses containing maize showed greater meltability than teff. Meltability could have been affected by the complexation of the different starches with monoglyceride or by proteolysis of the cheese matrix during storage. Storage time had a more significant effect on the firmness, softening point and meltability of all the imitation cheeses than the addition of starches as a fat replacer. All imitation cheeses were found to be softer and have lower softening points. Storage time showed an increase in meltabilty of all imitation cheeses except for the cheeses made with unmodified teff and teff modified with 1.5% monoglyceride. Confocal Laser Scanning Microscopy (CLSM) showed numerous small (10 micrometer) small fat globules in full fat imitation cheese, and more protein matrix than fat globules in the low calorie imitation cheeses. The fat globules seemed to get bigger as storage time increased. An increased band intensity seen with SDS-PAGE of full fat imitation cheese. This indicated that the softening of all the imitation cheeses over the storage time of 30 days could be at least partially due to proteolysis. Residual plasmin found in the rennet casein used to manufacture imitation cheeses is thought to be responsible. Teff and maize starches modified with monoglyceride have the potential to be used as fat replacers in imitation Mozzarella cheese as the texture, softening point and meltability remains close to that of natural Mozzarella cheese. This can decrease the calorific value of the cheese as well as the cost of manufacture.