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Fresh-cut leafy vegetables: oxalic acid an alternative to chlorine
Rocket and baby spinach are two leafy vegetables principally consumed as fresh-cut products, either alone or in a mixture with other vegetables. These leafy vegetables are very perishable, the shelf life is only 5–7 days when stored at 8C because of their high respiration rate. During storage, leaf color degrades rapidly as result of chlorophyll degradation, the loss of the normal green color is a limiting factor for marketability because it influences consumer choice
Maria Cefola and Bernardo Pace, scientists at Institute of Sciences of Food Production - National Research Council of Bari (Italy) have investigated for the first time the effect of postharvest treatment with oxalic acid (OA) on the overall quality of fresh-cut rocket and baby spinach.
These leafy vegetables are usually washed with hypochlorite solution, thus OA could be an innovative postharvest treatment alternative to chlorine, being OA a natural preservative, it can respond to consumer awareness of the use of chemically synthesized additives.
For the study, the leaves of rocket and baby spinach were dipped in 1 mM OA solution for 1 min and then stored for 6 days at 8°C. As control (CTR), the leaves of rocket and baby spinach were immersed in hypochlorite, as currently practised by fresh-cut industries.
Results showed that OA treatment significantly delayed deterioration during storage, with clear benefits for overall quality. Specifically, OA reduced the visual quality loss and yellowing of the leaves, slowing down the respiration rate, ammonia production, chlorophyll degradation and electrolyte leakage. In addition, the antioxidant activity and total phenol content were preserved by OA treatment.
Finally, OA reduced the mesophilic aerobic count, with a performance similar to that of hypochlorite washing. Total viable count was affected only by treatment and storage duration in both vegetables. At harvest, the initial counts were 5.5 (±0.2) and 6.5 (±0.3) log cfu/g in rocket and spinach leaves, respectively. In both vegetables, immediately after treatment, a mean reduction in total microbial count of about 1.8 and 1.5 log cfu/g was measured in samples dipped in hypochlorite (CTR) or OA, respectively. During storage, in both vegetables (both OA and CTR), an increase of about 2 log was observed.
The scientists conclude that the study demonstrates that OA can be used as a valid postharvest treatment in fresh-cut rocket and baby spinach leaves, with beneficial effects on quality parameters during storage. In the future, the effect of OA treatment on other leafy vegetables could be investigated.
The study was financed by MIUR Research Projects: “High-Convenience Fruits and Vegetables: New Technologies for Quality and New Products,” PON01_01435.
Results of the study are available online from 29 April at:
Source: Maria Cefola and Bernardo Pace, ‘Application of oxalic acid to preserve the overall quality of rocket and baby spinach leaves during storage’, 2015, Journal of Food Processing and Preservation, doi:10.1111/jfpp.12502
Institute of Sciences of Food Production, National Research Council
Via G. Amendola, 122/O,
Bari 70126, Italy
Ph.: +39 080 5929304
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