Postharvest changes in profiles of sugars, organic acids and tocopherols in leafy vegetables monitored by chromatographic techniques

After harvest, plants remain living organisms with the capacity to carry out metabolic processes. Thus, from the moment they are detached from the source of nutrients, they become entirely dependent on their own organic reserves [1]. Postharvest changes cannot be stopped, but they can be slowed within certain limits. Therefore, this study was conducted to evaluate the effects induced by storage in the profiles of sugars, organic acids and tocopherols of two leafy vegetables. Wild samples of watercress (Nasturtium officinale R. Br.) and buckler sorrel (Rumex induratus Boiss. & Reut.), from the Northeastern region of Portugal, were analyzed after harvest (control) and after storage in sterilized packages (using the passive modification mode) at 4ºC for 7 or 12 days, respectively. Analyses were performed by high-performance liquid chromatography (HPLC) using different detectors, i.e., a refraction index detector (RID) for free sugars, a photodiode array detector (PDA) for organic acids, and a fluorescence (FP) detector for tocopherols. The storage time decreased the levels of fructose, glucose and total sugars in both leafy vegetables and increased the total organic acids content. The decrease of these sugars can be related to its use by the plant to produce the required energy. Ascorbic acid was detected in buckler sorrel and decreased with storage; while the amount of malic acid increased in both species. Curiously, all the tocopherol isoforms increased in watercress, while buckler sorrel just present higher values of γ- and δ- tocopherols. In fact, the de novo synthesis of these bioactives compounds can be a plant strategy to fight against the reactive species that are produced during storage. The knowledge of the behavior of these compounds during storage that was achieved with this study [2] may contribute to the development of more effective preservation strategies for leafy vegetables.

Valorização de produtos de montanha pela utilização de tecnologias de processamento não convencionais

Os vegetais embalados prontos a comer têm tido uma crescente aceitação por parte do consumidor por atenderem aos requisitos contemporâneos de conveniência, segurança e salubridade. O crescimento deste setor tem levado à introdução de novos produtos e à adoção de tecnologias de conservação mais eficientes, seguras e sustentáveis [1]. O consumidor procura também alimentos com características organoléticas diferenciadas das dos alimentos habitualmente consumidos diariamente. A recuperação do uso de Rumex induratus Boiss. & Reut. (azedas) e Nasturtium officinale R. Br. (agrião) poderá responder a esta procura, aliando garantia de qualidade e inovação. Visto a maioria dos tratamentos convencionais ser ineficaz em assegurar segurança sem comprometer a qualidade, e dada a preocupação em torno dos agentes químicos vulgarmente utilizados, a irradiação de alimentos e o embalamento em atmosfera modificada têm emergido como alternativas seguras e eficazes [1-4]. Neste sentido, este estudo teve como objetivo avaliar a eficácia de diferentes atmosferas de embalamento e de diferentes doses de radiação ionizante na conservação da qualidade destas espécies durante o armazenamento refrigerado. O uso sustentável de produtos vegetais para a recuperação de biomoléculas ou produção de ingredientes funcionais de valor acrescentado é uma estratégia útil que pode ajudar a enfrentar os desafios societais deste século. Atualmente é originada uma grande quantidade de resíduos de tomate (Lycopersicon esculentum Mill.) fresco durante as várias etapas do seu ciclo produtivo, desde a cultura até ao armazenamento e venda [5]. Estes resíduos são ricos em licopeno e vitaminas, mas também em compostos fenólicos [6,7]. Estes compostos bioativos estão envolvidos na prevenção de várias patologias humanas e são de elevada importância para a indústria alimentar, farmacêutica e cosmética. Visto os métodos convencionais utilizados para a extração destas biomoléculas apresentarem várias desvantagens, novas tecnologias mais eficientes e sustentáveis têm vindo a ser adotadas. Neste sentido, este trabalho teve como objetivo otimizar as condições de extração assistida por tecnologia micro-ondas de antioxidantes hidrofílicos e lipofílicos e dos ácidos fenólicos e flavonoides maioritários da variedade de tomate redondo utilizando a metodologia de superfície de resposta (RSM).

Postharvest quality changes in fresh-cut watercress stored under conventional and inert gas-enriched modified atmosphere packaging

The effect of modified atmosphere packaging (MAP) on the postharvest quality of fresh-cut watercress (Nasturtium officinale R. Br.) stored at 4 ºC for 7 d was studied. A portion of watercress was immediately analyzed (non-stored control) and the remaining fresh material was stored packaged under atmospheres enriched with N2, Ar, air, or vacuum. The analyzed parameters included colour, total soluble solids, pH, macronutrients, the individual profiles of sugars, organic acids, tocopherols and fatty acids, and total phenolics and flavonoids. Furthermore, four in vitro assays were performed to evaluate the antioxidant activity. After assessing the effect on individual quality parameters, it was possible to conclude that air was the less efficient atmosphere in preserving quality attributes of the non-stored control samples during cold storage. In turn, Ar-enriched MAP was the most suitable choice to preserve the overall postharvest quality. The present study also highlighted the nutritional and antioxidant properties of watercress, as well as the interest of its inclusion in human diets.

Suitability of gamma irradiation for preserving fresh-cut watercress quality during cold storage

The suitability of gamma irradiation (1, 2 and 5kGy) for preserving quality parameters of fresh-cut watercress (Nasturtium officinale R. Br.) during storage at 4±1°C for 7d was investigated. The storage time decreased the protein content and the main carbohydrates, and increased the levels of malic and fumaric acids, sucrose and mono- and polyunsaturated fatty acids (MUFA and PUFA). The different irradiation doses did not caused any significant colour change. In general, the 2kGy dose favoured PUFA and was the most suitable to preserve the overall postharvest quality of fresh-cut watercress during cold storage. In turn, the 5kGy dose better preserved the antioxidant activity and total flavonoids and favoured MUFA, tocopherols and total phenolics, thus originating a final product with enhanced functional properties. Therefore, the suitability of gamma irradiation for preserving fresh-cut watercress quality during cold storage was demonstrated.