The Physicochemical and Sensory Properties of Fruit and Vegetable Fibre Suspensions - The Effect of Fibre Processing and its Addition to Low-Fat Sausages

Abstract: Due to the health effects of dietary fibre, as well as its water-holding capacity (WHC), food products are commonly fortified with fibre-rich sources. However, to be able to design food products with specific textural properties that also appeal to the consumer, it is important to understand and to characterise the physicochemical and chemical properties of the fibre. In this study the composition of dietary fibre, the solubility of pectin, the microstructure, rheological properties and water-holding capacity, as well as the sensory properties of fruit and vegetable suspensions and fibre-amended sausages, have been investigated. The plant materials used were tomato, apple, carrot and potato pulp. The variation in these properties following different kinds of processing, i.e. homogenisation and heat treatment, was also studied. The fibre suspensions responded differently to high-pressure homogenisation. This could be due to the fundamentally different inherent microstructures of the samples, probably originating from different proportions of soluble and insoluble fibre. A high content of insoluble pectin and a high perceived crispiness/graininess was found in suspensions with a microstructure consisting of large cell clusters and aggregates (carrot and potato pulp). The micro¬structure of these suspensions is degraded to smaller clusters by homo¬genisation, but retains their original cellular shape. However, suspensions with a microstructure consisting of single cells and cell fragments (tomato and apple), were more easily degraded by homogenisation, and contained lower amounts of insoluble pectin. The latter type of microstructure exhibited a higher WHC, elastic modulus and sensory perceived melting and slipperiness. The main effect of heat treatment was on the solubility of the dietary fibre. In carrot and apple suspensions where β-elimination was favoured by heating, an increase was seen in the amount of soluble pectin together with a decrease in the mean particle size of the insoluble fibre. With the decrease in the insoluble material, a significant decrease in the WHC was seen for both apple and carrot. Heat-treated potato pulp suspensions were affected differently, since starch remaining in the matrix started to swell, which led to a difference in the particle size distribution and morphology. There was also a significant increase in WHC with heating, probably resulting from the swelling of the starch. Low-fat sausages containing potato pulp exhibited greater firmness than the sausage without any fibre, according to a compression test. It is suggested that the high content of insoluble fibre in the potato pulp forms a strong fibrous network in the meat protein network of the sausages, thereby increasing the firmness.