Consumers and vegetables: effects of domestic processing on sensory and health properties

The quality of foods e.g. vegetables at the time of consumption depends on the post-purchase handling conditions especially by domestic processing. On the one hand, from the consumer’s perspective, domestic processing i.e. cooking improves the sensory acceptability of vegetables. On the other hand, from the food technologist’s perspective, nutrients like vitamins and phytochemicals are degraded (though bioaccessibility can increase) by various processing conditions. An approach that integrates consumer and food technologist perspectives is necessary to have processed vegetables that are acceptable by consumers but are higher in nutrients. Therefore, the Consumer Orientated Food Technology (COFT) approach is introduced in this thesis. The COFT approach aims to redefine the ‘current’ vegetable product into a ‘new’ product that aligns with consumer sensory preferences but possesses a higher amount of nutrients. The first objective of this thesis was to evaluate research methods: in-home observations, observations using cameras in a model-kitchen and self-reporting questionnaire for their reliability, validity and practicality for collection of data on consumer (n = 25) behaviour towards broccoli. All three methods were found to be test-retest, inter-observer, intra-observer and parallel-form reliable and face, concurrent and content valid. However, due to wide inter-individual variability in behaviour towards domestic processing of broccoli, self-reporting questionnaire was established as the most practical among these three research methods. The second aim was to use this research method – self-reporting questionnaire – to identify consumer common motives and behaviour (domestic processing conditions) towards broccoli (n = 542) and carrots (n = 348) among Dutch study sample; and to identify consumer groups with comparable motives and behaviour. Hierarchical cluster analysis, performed separately for both vegetables, identified three groups of consumers: texture-orientated (56-59 %), health-orientated (20-30 %) and taste-orientated (8-26 %) for both vegetables. The third aim was to study the influences of the above identified common domestic processing conditions on sensory and health attributes of broccoli and carrots. Firmness, colour and amount of phytochemicals (glucosinolates in broccoli and carotenes in carrots) were analysed instrumentally. Firmness, greenness, juiciness, flavour, sweetness, bitterness were measured on a 9-point hedonic scale and overall liking was measured on a 100 mm Visual Analogue Scale using an untrained consumer panel (n = 100). Steaming compared boiling with a cold (water) start and hot (water) start showed least losses in glucosinolates from broccoli and β-carotenes from carrots at different cooking times. It was found that for optimal liking the texture of the cooked vegetables should be in the range of medium firmness. In addition, consumers did not show any statistically significant differences in liking between steamed and boiled vegetables. The fourth aim was to optimise the processing conditions that will yield vegetables with equal liking but with higher amount of phytochemicals. Using mathematical modelling, optimised processing conditions are proposed for consumers who cook broccoli till low firmness is achieved (soft texture). These simulations show that adapting temperature, time and amount of water used during boiling will result in at least 18 % higher amount of glucosinolates and will still give soft textured broccoli.