Browsing by Author "Petrus, Alicia"
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- ItemUse of heat treatment to improve the aroma and flavour of Cyclopia products(Stellenbosch : Stellenbosch University, 2021-04) Petrus, Alicia; Joubert, Elizabeth; Moelich, Erika Ilette; De Beer, Dalene; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: There is a need for efficient use of available honeybush plant material through the reduction of waste caused by processing and rejection due to poor quality resulting from production errors. In the present study, heat processing was used to convert an ultrafiltration waste stream into a food flavour ingredient. The retentate waste stream obtained from the ultrafiltration of C. genistoides extract was subjected to a range of temperature-time combinations (80°C for 2, 4, 8 and 16 h; 90°C for 2, 4, 6 and 8 h) to determine conditions for optimal aroma and flavour development when reconstituted to “cup-of-tea” strength and subjected to descriptive sensory and physicochemical analysis. An increase in heating time of the retentate increased the colour development of the beverage and the intensities of fruity and sweet attributes, while decreasing its turbidity, bitterness, astringency and the intensities of taints. Heating induced degradation of phenolic compounds, which followed first order reaction kinetics. Based on the sensory profile, the optimum heating conditions were 80°C/4 h and 90°C/4 h. Subsequent validation of these conditions on other batches of retentate (n = 10) showed that 90°C/4 h was more effective for the development of desirable fruity and sweet attributes, though degradation of phenolics was more extensive. The current high-temperature oxidation (“fermentation”) step used in the production of traditional honeybush tea is a slow process (16 h and longer), leading to poor control and product rejection due to poor quality. Ultra-high temperature oxidation (UHTO) of C. genistoides and C. subternata was investigated with the aim to shorten the processing time. Dried, green plant material, rehydrated to ca. 53% moisture content, was autoclaved at 110°C (2, 4, 6 h), 120°C (1, 2, 3 h) and 130°C (0.5, 1, 1.5 h), while conventionally prepared tea (80°C/24 h and 90°C/16 h) served as controls. The effect of UHTO on the sensory and physicochemical characteristics of the “cup-of-tea” infusions was assessed using descriptive sensory analysis and instrumental methods. UHTO increased the intensities of fruity and sweet attributes, but if the heat treatment was too severe, samples developed a “burnt caramel” taint, while samples treated for the shortest period at each temperature retained a “green” honeybush-like character. The dark-brown colour of the UHTO samples intensified with heating time. UHTO infusions were more turbid than the controls. Similar trends were observed for the two Cyclopia species, but C. genistoides needed more time to develop optimal sensory characteristics. The optimum temperature × time regimes for C. subternata and C. genistoides were 120°C/2 h and 120°C/3 h respectively. Validation of UHTO conditions was performed on other batches (n = 10) of C. subternata, with oxidation at 90°C/16 h serving as a control. Both fresh and rehydrated, dried green plant material were used to determine the effect of preservation (drying) of the plant material prior to oxidation on the quality of the beverage. Quality was assessed similarly to the optimisation experiment. Preservation had no detrimental effect on the sensory profile of the infusions and they were less turbid, while their colour was slightly lighter and less saturated.