Effects of steam treatment and storage on green honeybush quality

[摘要] ENGLISH ABSTRACT: Application of steam treatment to green Cyclopia maculata and C. longifolia to modulate their aromaand flavour profile, without detrimental effects on colour and individual phenolic content, wasinvestigated. Steam treatment (96 °C, atmospheric pressure) of different time periods was appliedto the shredded, fresh plant material before drying (STBD; 0, 30, 60, 90 and 120 s) or the herbal teaproduct after drying (STAD; 0, 1, 2, 3, and 4 min). Steam treatment of 60 s or longer resulted in asignificant (p < 0.05) decrease in vegetative ('green grass' and 'hay/dried grass') and cereal('oats/porridge/grains') aroma and flavour intensities, with an increase in some fruity ('tropical fruit'and 'guava') and 'fruity-sweet' aroma intensities. These changes manifested to a greater degree forplant material subjected to STBD, while they were less prominent for C. longifolia compared toC. maculata. Additionally, 19 aroma compounds were instrumentally identified in the volatile fractionof C. maculata infusions prepared from STBD plant material. Of these, seven correlated well withgreen honeybush vegetative and cereal aroma attributes associated with unsteamed samples.Steaming thus resulted in the rapid loss of some of these highly volatile 'green'-associated aromacompounds. Steam treatment of more than 60 s, regardless of STBD or STAD, was not detrimentalto green colour, and individual phenolic content was not greatly affected. The 30 s STBD treatmentof C. maculata, however, led to the rapid loss of green colour and oxidation of phenolic compounds,without considerable aroma improvement. This highlights the need for process control during greenhoneybush production. Storage stability of steamed (60 s, STBD) and unsteamed green C. maculata wasinvestigated under low (0 °C; moisture impermeable packaging) and normal (25 °C at 60% relativehumidity (RH); semi-moisture-permeable sachets) temperature storage conditions (LTS and NTS,respectively) over 6 months and high temperature storage (HTS) conditions (40 °C at 75% RH; semimoisture-permeable sachets) for 1 month. HTS conditions, after 1 month, seemed to emulatechanges occurring over 6 months at NTS conditions, with little change detected at LTS conditions.Despite noticeable green colour loss over the respective storage periods at NTS and HTS conditions,individual phenolic compounds were not severely affected. NTS and HTS led to the progressivedevelopment of sought-after fermented honeybush sensory attributes, especially in unsteamedsamples. These include prominent fruity ('stewed fruit', 'apricot jam' and 'marmalade') aromas andflavours, 'general sweet' and 'fruity-sweet' aromas and a sweeter taste. The collated descriptive sensory data were used to generate a preliminary sensory wheel forgreen honeybush aroma, and another for flavour, taste and mouthfeel. The sensory profile of greenhoneybush was finally described as a dominant vegetative aroma and flavour, prominent sweetassociatedand slightly fruity aroma, with sweet and notably bitter tastes and an astringent mouthfeel.By combining the sensory data, it was clear that the major effects of storage outweighed those ofsteam treatments, suggesting that storage of 3 to 6 months may improve sensory quality, although colour may be slightly compromised. Immediate sensory manipulation and thus improvement,however, may be achieved to a lesser degree in the short term by STBD.

[发布机构] Stellenbosch University