Abstract
Asparagus is a perennial crop with a short UK harvest season. Methods to extend the storage life of asparagus have proven difficult. To gain insight into the physiological (viz. colour, respiration rate, cutting energy, and stiffness measured using laser Doppler vibrometry), and biochemical (viz. sugars, ascorbic acid, and abscisic acid and its catabolites) changes throughout the UK season, two cultivars were harvested weekly and stored under shelf life conditions (7 °C). Results were compared to spears (plus one additional cultivar) cold stored (1 °C) for three weeks followed by one week of shelf life. Concentrations of sugar, abscisic acid (ABA) and catabolites at harvest were subject to seasonal variation, directly affecting storage potential. A generalised linear model with stepwise feature selection was applied to select the most important parameters for the prediction of total sugars and phaseic acid (PA). More favourable growing conditions at harvest increased sugars and lowered ABA content and catabolites, which coincided with better maintenance of spear quality during storage; including maintaining textural characteristics. Storage time had a negative impact on spear texture and sugar content, with cutting energy increasing and stiffness decreasing both during cold storage and subsequent shelf life. A partial shift in sugar biosynthesis occurred during shelf life increasing sucrose concentrations. Results suggest that the temporal flux in ABA and catabolites, and individual sugars could be used to model storage potential of asparagus spears.
Highlights
The UK asparagus (Asparagus officinalis) season is relatively short and typically lasts from April to June, with a late harvest in September accomplished by using a reverse season technique (Hart, 2015)
The UK season was found to have a limited effect on asparagus colour where L* and C* remained stable with no significant differences between cultivar or harvest week, with the exception of C* in the tip, which showed some minor fluctuation over the course of the season in both cultivars
Cutting energy tended to increase towards the end of shelf life in samples of both cultivars, but the observed increase was most pronounced on the second week of harvest (Supplementary material 2)
Summary
The UK asparagus (Asparagus officinalis) season is relatively short and typically lasts from April to June, with a late harvest in September accomplished by using a reverse season technique (Hart, 2015). The appearance of the spear (shape, size, girth, and colour) is considered the most critical quality attribute for commercial grading standards; whereas organoleptic attributes (texture, taste, aroma, flavour and bitterness) are important features used by consumers to assess quality (Siomos, 2018). Cold storage has been reported to maintain lower respiration rate and suppress the catabolism of quality-related compounds (Lipton, 1990), but it can promote lignification (Toscano et al, 2018). During spear elongation in the field, spear tips have been reported to maintain high concentrations of ABA compared to other parts of the spear (Kojima et al, 1993), but to date there is little understanding of how ABA concentrations change during the harvest season and the potential impact this may have on asparagus storability
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