Effect of cultivar and growth region on the mechanical and biochemical properties of canned baked beans

Canned baked beans are the most widely consumed legume product in UK. The canning quality of the beans will significantly influence consumer acceptability and the commercial sales. In this project, the mechanical, microstructure and biochemical properties of several cultivars of navy beans which were grown in different regions of North America were investigated in order to identify factors that could help the industry to predict canning quality.
A texture analyser (TA.XT plus) was used to measure the mechanical properties of the beans, either as single or a batch of beans. Beans from cultivar 2 and region C had significant firmer texture, and region affected firmness more than cultivar. Beans canning in tomato sauce softened by 98% compared to blanched beans, and achieved 50% firmer texture than those canned in brine or water. The mechanical properties may have been influenced by the structural properties. Cytochemical and immunofluorescence microscopy was used to visualise the microstructure of the beans’ skin and cotyledon, with a focus on the localisation of cell wall polysaccharides. Cell adhesion in the cotyledon was mediated by un-methyl esterified HG localised in the middle lamella, which was not completely lost upon canning, most likely due to osmotic pressure from the sauce. However the differences between cultivar and region could not be quantified using the microscopical techniques. Exchange of polysaccharides was observed between the bean and the sauce. Analytical biochemical methods were used to analyse the composition of the beans. Canned baked beans were rich in dietary fibre (10.8%-16.4%) which was composed of cell wall polysaccharides and undigested starch. Firmer beans were found to contain more dietary fibre (r=0.85), most particularly cell wall neutral sugar (r=0.82) composed of arabinose, galactose, xylose and mannose. Therefore, cell wall structure and composition are affected by cultivar, growth region and processing conditions, and are very important in determining the textural properties of canned baked beans. However, of all the physical, mechanical and biochemical measures studied in this thesis, only one (drained weight) was highly correlated with the other measures, and significantly affected by cultivar and region. Therefore, drained weight may be the best predictor of textural quality.