From the field to the table: ionizing radiation as a feasible postharvest treatment for fresh and dried plant foods

Food irradiation is a treatment that involves subjecting in-bulk or packaged food to a controlled dose of ionizing radiation, with a clearly defined goal. It has been used for disinfestation and sanitization of food commodities and to retard postharvest ripening and senescence processes, being a sustainable alternative to chemical agents 1 . Doses up to 10 kGy are approved by several international authorities for not offering negative effects to food from a nutrition and toxicology point of view 2 . However, the adoption of this technology for food applications has been a slow process due to some misunderstandings by the consumer who often chooses non-irradiated foods. In this study, the effects of the ionizing radiation treatment on physical, chemical and bioactive properties of dried herbs and its suitability for preserving quality attributes of fresh vegetables during cold storage were evaluated. The studied herbs, perennial spotted rockrose (Tuberaria lignosa (Sweet) Samp.) and common mallow (Malva neglecta Wallr.) were freeze-dried and then irradiated up to 10 kGy in a Cobalt-60 chamber. The selected vegetables, watercress (Nasturtium officinale R. Br.) and buckler sorrel (Rumex induratus Boiss. Reut.) were rinsed in tap water, packaged in polyethylene bags, submitted to irradiation doses up to 6 kGy and then were stored at 4 C for a period of up to 12 days. Physical, chemical and bioactive parameters of irradiated and non-irradiated samples were evaluated using different methodologies the colour was measured with a colorimeter, individual chemical compounds were analyzed by chromatographic techniques, antioxidant properties were evaluated using in vitro assays based on different reaction mechanisms, and other quality analyses were performed following official methods of analysis. The irradiation treatment did not significantly affect the colour of the perennial spotted rockrose samples, or its phenolic composition and antioxidant activity 3 . Medium doses preserved the colour of common mallow and a low dose did not induce any adverse effect in the organic acids profile. The green colour of the irradiated vegetables was maintained during cold storage but the treatment had pros and cons in other quality attributes. The 2 kGy dose preserved free sugars and favoured polyunsaturated fatty acids (PUFA) while the 5 kGy dose favoured tocopherols and preserved the antioxidant properties in watercress samples. The 6 kGy dose was a suitable option for preserving PUFA and the ω-6 ω-3 fatty acids ratio in buckler sorrel samples. This comprehensive experimental work allowed selecting appropriate processing doses for the studied plant foods in order to preserve its quality attributes and edibility.

HPLC-DAD-ESI/MS analysis of phenolic compounds in four tomato varieties and evaluation of the antioxidant capacity

Tomato (Lycopersicon esculentum L.) is the second most important vegetable crop worldwide and a key component in the so-called “Mediterranean diet”. In the Northeastern region of Portugal, local populations still prefer to consume traditional tomato varieties which they find very tasty and healthy, as they are grown using extensive farming techniques. A previous study of our research team described the nutritional value of the round (batateiro), long (comprido), heart (coração) and yellow (amarelo) tomato varieties [1], but the phenolic profile was unknown until now. Thus, the objective of this study was to characterize the phenolic profiles of these four tomato farmers’ varieties by using HPLC-DAD-ESI/MS and evaluate its antioxidant capacity through four in vitro assays based on different reaction mechanisms. A cis p-coumaric acid derivative was the most abundant compound in yellow and round tomato varieties, while 4-O-caffeolyquinic acid was the most abundant in long and heart varieties. The most abundant flavonoid was quercetin pentosylrutinoside in the four tomato varieties. Yellow tomato presented the highest levels of phenolic compounds, including phenolic acids and flavonoids, but the lowest antioxidant activity. In turn, the round tomato gave the best results in all the antioxidant activity assays. This study demonstrated that these tomato farmers’ varieties are a source of phenolic compounds, mainly phenolic acid derivatives [2], and possess high antioxidant capacity [1]; being thus key elements in the diet to prevent chronic degenerative diseases associated to oxidative stress, such as cancer and coronary artery disease.