Physical hurdles to enhance watercress' quality and safety: Effects on chemical and bioactive parameters
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abstract
The hurdle concept provides a framework for combining a number of milder preservation
factors (hurdles) in order to achieve an enhanced level of product safety and stability. For
fresh vegetables such as watercress (Nasturtium officinale R. Br.), characterised by a
reduced shelf-life, some of these hurdle have focused on the use of modified atmosphere
packaging (MAP) combined with other physical or physicochemical factors (Alexandre et
al., 2011; Silveira et al., 2014). Thus, in the present work, the combined effects of passive
MAP, gamma irradiation and refrigerated storage on chemical and bioactive quality
parameters of watercress were evaluated. Wild specimens were gathered in the Northeast
region of Portugal, rinsed in tap water and a portion was immediately analysed (control).
The remaining fresh material was packed under passive MAP, exposed to 1, 2 and 5 kGy
of y-rays in a 6°Co chamber and stored at 4 oc for 7 days. Non-irradiated samples followed
all the assays. Sugars, fatty acids, tocopherols and organic acids were analysed by
chromatographic techniques. Phenolics and flavonoids were determined by
spectrophotometer methods. The antioxidant activity was evaluated in hydroalcoholic
extracts using four distinct in vitro assays. In general, the sucrose and organic acid levels
increased in stored samples. The 5 kGy dose protected MUF A (monounsaturated fatty
acids), while the 2 kGy dose was effective in favouring PUF A (polyunsaturated fatty
acids). In either case, the hurdle treatment allowed obtaining watercress samples with a
healthier fatty acids profile, as also verified in the increased PUF A/SF A (saturated fatty
acids) ratio. Concerning tocopherols, the most relevant result was the effect achieved with
the 5 kGy dose, particularly owing the contributions of a- (the major isoform) and ytocopherols.
The same dose also allowed the best results in maintaining the antioxidant
activity, as well as in phenolics and flavonoids. Through Linear Discriminant Analysis it
was concluded that 2 kGy is the preferable hurdle to maintain the original characteristics of
watercress. Nevertheless, the 5 kGy dose should also be considered when aiming to obtain
a final product with healthier properties. Thus, this study highlighted the suitability of the
applied hurdles to enhance watercress functionality and shelf-life.
