Effects of different processing technologies on chemical and antioxidant parameters of Macrolepiota procera wild mushroom

Highlights

• Different processing technologies were applied to Macrolepiota procera samples.

• Freezing and drying caused significant differences in chemical parameters.

• Gamma irradiation retained the chemical profile of fresh samples.

Abstract

Mushrooms are very perishable foods, demanding for processing technologies that retain chemical and nutritional characteristics of fresh forms. In this work, the influence of freezing, drying and gamma irradiation on chemical parameters and antioxidant potential of Macrolepiota procera was assessed through one-way ANOVA complemented with principal component analysis. Proximate composition was evaluated by AOAC procedures, while fatty acids, tocopherols and free sugars were determined using chromatographic techniques. Antioxidant activity was measured using in vitro assays. M. procera samples have low energetic values, with moisture and carbohydrates as major nutrients. Linoleic, palmitic and oleic acids were the major fatty acids; δ-tocopherol was the prevalent isoform in fresh, frozen and irradiated samples, while β-tocopherol predominated in dried samples. Trehalose was the most abundant sugar in fresh and irradiated samples, whereas mannitol predominated in frozen and dried samples. Dried samples gave higher DPPH scavenging activity and β-carotene bleaching inhibition; freeze and irradiated samples showed higher reducing power and TBARS formation inhibition, respectively. Overall, freezing and drying caused significant differences in chemical parameters. On the other hand, gamma irradiation revealed the highest capacity to retain chemical profile of fresh samples, which highlights its potential to be explored and validated as an alternative conservation methodology.

Introduction

Mushrooms are widely appreciated for their unique taste and flavour, but also for their nutritional (Kalač, 2009) and medicinal properties, such as anti-inflammatory, anti-diabetic, antibacterial and antitumor, attributed to the presence of bioactive metabolites (e.g. phenolic compounds, terpenes, steroids and polysaccharides) (Ferreira et al., 2010, Poucheret et al., 2006). In particular, edible mushrooms can be a source of nutraceuticals with important antioxidant properties, which can positively influence the oxidative stress in cells and related diseases (Ferreira, Barros, & Abreu, 2009).

Nevertheless, mushrooms are one of the most perishable food products and tend to lose quality immediately after harvest. The shelf life is reduced due to post-harvest changes, namely browning, cap opening, stipe elongation, cap diameter increase, weight loss and texture damage, related to their high respiration rate and moisture, relatively high protein content, and lack of physical protection to avoid water loss or microbial attack (Fernandes, Antonio, Oliveira, Martins, & Ferreira, 2012). Therefore, mushrooms are mainly used in the processed form (Jaworska & Bernás, 2009).

Extending shelf-life is an imperative factor to increase the profitability and availability of any food product, since it offers the possibility of developing markets at a greater distance (Akram & Kwon, 2010), but the applied technology should not act itself as a source of chemical modifications.

Drying is the most common method for preserving mushrooms (Giri & Prasad, 2007) and freezing is becoming increasingly popular (Jaworska and Bernás, 2009, Jaworska and Bernás, 2010). Drying is a comparatively cheaper method (Rama and Jacob, 2000, Walde et al., 2006), while food freezing is among the most efficient and adequate preservation methods (Haiying, Shaozhi, & Guangming, 2007). The main advantage of freezing is that it allows the best retention of nutritional value as well as sensory qualities such as colour, aroma, taste and texture; during freezing most of the liquid water changes into ice, which greatly reduces microbial and enzymatic activities (Haiying et al. 2007).

Food irradiation has also been suggested as a safe and adequate process to maintain and increase the food shelf life (WHO, 1994). This physical method of conservation involves exposing a product to ionizing radiation, in a controlled dose and irradiation time (Akram and Kwon, 2010, Fernandes, Antonio, Oliveira, et al., 2012). The maximal recommended dose for extending the shelf-life of fresh mushrooms is 3 kGy (ICGFI, 1999).

Many studies have applied gamma irradiation to a range of mushrooms including cultivated (Jiang et al., 2010, Sommer et al., 2010) and, more recently, wild species (Fernandes, Antonio, Barreira, Botelho, et al., 2012, Fernandes, Antonio, Barreira, Oliveira, et al., 2012). In those two studies of our research group, the effects of gamma irradiation on chemical composition, antioxidant activity and physical parameters of fresh Lactarius deliciosus wild edible mushroom were evaluated, being concluded that up to 1 kGy this technology was effective in maintaining chemical composition and controlling the deterioration of fresh samples.

The main objective of the present study was to assess the effects of different processing technologies (freezing, drying and gamma irradiation) on chemical and antioxidant parameters of the wild mushroom Macrolepiota procera, in order to select the most suitable solution to be applied in future studies related to its preserving ability.