Cereal Dietary Fibre - Physicochemical Properties and Suitability for Addition to Low-Fat Meat Products
Sammanfattning: It is well known that dietary fibre is good for the health. Cereals, and in particular the outer parts of the cereal kernels, are rich in dietary fibre. Rye bran, wheat bran, oat bran and barley fibre have been investigated regarding their suitability as additives in low-fat meat products. Two types of meat products, frankfurter-type sausages and meatballs have been evaluated in this thesis. In the sausages the meat protein network governs the texture and water-holding properties, whereas the meatballs have a more particulate structure, where a more crumble texture is perceived and the water-holding capacity is lower. Cereal bran particles can be difficult to add to a food-system without also adding a disagreeable sensation of grittiness. Evaluations of how the size and concentration of small rye bran particles in a continuous phase of varying viscosity influence the sensory perception of grittiness were performed. The threshold for the sensation of grittiness resulting from rye bran particles in a starch gel was very low and independent of the particle size. The particles were detected already at concentrations of 0.1-0.3%, despite the fact that they were so small (20-180 μm). The rheological properties of the suspension medium did not influence the detection threshold. One reason for this obvious perception of grittiness of rye bran particles could be their irregular shape and hardness. One way of altering these adverse properties of the bran particles could be by treating them with hydrolytic enzymes. The xylanases and endoglucanases evaluated in this thesis did not increase the water-holding capacity of the rye or wheat bran or the viscosity of the aqueous phase. The water-holding capacity was probably reduced because of the lower amount of insoluble material after solubilization by the enzymes, while the lower viscosity showed that the solubilized dietary fibre were degraded into smaller molecules which could no longer contribute to the viscosity. Due to the gelling ability of the inherent β-glucan of the oat bran upon heating, it was found to be the most suitable for addition to low-fat sausages. These sausages exhibited low process and frying losses, together with high values of both firmness and sensory acceptance. The barley fibre gave a poor texture of the sausages and was the least preferred. This barley β-glucan could not form a gel, probably because of a smaller molecular weight and a less favourable structure, compared to the oat β-glucan. Rye bran is suitable for addition to meatballs, probably due to its particulate nature, which is more acceptable in this type of meat product, where the gelling properties are not as important as in sausages.
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