Abstract:
The increasing rate of obesity and its related diseases (cancers, heart disease and diabetes) has become a global health issue. Dietary fat is highlighted as one of the critical risk factors contributing to this problem. Reduction of the fat content of popular food products, in an attempt to reduce fat intake without compromising the desirable sensory properties provided by fat, is challenging. This study characterised two lipid-modified maize starches (maize starch modified with 1.5 % stearic acid and maize starch modified with 2 % monoglyceride) produced by incorporating food-friendly lipids into maize starch through wet-heat processing. Sunflower oil was substituted with these complexes in the production of reduced-fat mayonnaise-type emulsions, at 0 % (control), 50 %, 80 % and 98 % oil replacement, with qualities similar to that of full-fat mayonnaise. The effect of the substitution on the rheological, lubricating, descriptive sensory profile (panel, n =10), consumer acceptance (consumers, n = 207), and accelerated shelf-life (40 °C with 24 h UV illumination) of the reduced-fat mayonnaise-type emulsions was determined.
The lipid-modified starches were non-gelling, glossy, smooth, creamy, easy-to-swallow and had good lubricating properties. These attributes could be ascribed to the formation of amylose-lipid complexes during the modification process of maize starch with stearic acid and monoglyceride. The formation of amylose-lipid complexes prevented further aggregation of amylose double helixes from forming crystalline structures and made amylose less available for junction zone formation and molecular entanglement, resulting in non-gelling starches. The lower friction coefficient values recorded for the starch-lipid complexes could be due to the nanoparticle sizes (2.4–6.7 nm) of the amylose-lipid complexes. The nanoparticle nature of the amylose-lipid complexes possibly increased the volume to surface area ratio of the complexes making them more available to act as a layer of lubricant. Lower friction coefficient implies increased lubricating effect, which enhances the sensory perception of fat-related attributes, thus influencing the perceived smoothness, creaminess, and easy-to-swallow nature of the starch-lipid complexes.
All the reduced-fat mayonnaise-type emulsions were smooth, melting, and easy-to-swallow and the starch/monoglyceride emulsions had a higher thickness, creaminess and mouth-coating. The higher thickness and mouth-coating can be attributed to the availability of uncomplexed amylose, which is more abundant in the starch/monoglyceride fat-replacer than in starch/stearic acid one, to form junction zones and molecular entanglements. The amylose-lipid complexes present in the fat replacers provided the emulsions with a non-gelling highly viscous matrix that stabilised the residual oil droplets in the reduced-fat mayonnaise-type emulsions. All the reduced-fat mayonnaise-type emulsions showed good lubrication with starch/monoglyceride emulsions showing more sensitivity to coalescence and gave rise to lower friction than starch/stearic acid emulsions.
The lipid-modified starches did not effectively retard the rate of lipid oxidation in the reduced-fat mayonnaise-type emulsions at accelerated storage. Hence the oil droplets could easily interact with the aqueous phase pro-oxidants, thus increasing the rate of oxidation. The possible increase rate of oxidation could also be due to the presence of liberated iron ions, Fe2+, from the egg yolk present as a stabiliser in the aqueous phase at the lower pH (< 4). At 50 % probability of consumer acceptance, the reduced-fat mayonnaise-type emulsion containing 80 % starch/monoglyceride was the most acceptable and had a predicted accelerated shelf-life beyond the 35 storage days.
The study has demonstrated the effective use of the two novel fat replacers to replace up to 80 % sunflower oil in the production of reduced-fat mayonnaise-type emulsions without compromising the desirable in-mouth textural properties of smoothness, creaminess, melting and mouth-coating. These fat replacers can be produced on a large scale and used as ingredients in commercial applications to improve the in-mouth textural properties of reduced-fat foods.
