Controlled nitrogen atmosphere for the preservation of functional molecules during silos storage: A case study using old Italian wheat cultivars

Highlights

• The use of a controlled atmosphere preserves the nutraceutical features of old wheat varieties.

• After 12 months of silos storage, the content of bound antioxidants drops.

• The content of free antioxidants and polyphenols, both free and bound, is not affected by long-term storage.

• The content of vitamin E follows the trend of bound antioxidants.

• The use of a controlled atmosphere slows down the loss of vitamin E.

Abstract

In the last decades, finding new methods to preserve the quality of wheat during post-harvest storage has become of primary importance to guarantee high-quality food products. Attacks by rodents and microorganisms, as well as humidity and high temperatures, are well-known factors affecting the qualitative and quantitative features of stored grains. The use of a controlled atmosphere saturated with different gases (such as carbon dioxide-CO₂ and nitrogen-N₂) is known to decrease the growth of microorganisms. Furthermore, the use of N₂ is free of pollutants, thus being an environmental-friendly method. In this study, the use of a controlled atmosphere saturated with N₂ was investigated as a method to preserve the nutraceutical qualities in two old Italian wheat cultivars (i.e. Verna and Cappelli). In particular, vitamin E (α-tocopherol), polyphenols and antiradical activity were quantified to highlight the differences between traditional storage methods and the use of a controlled atmosphere saturated with N₂. The data obtained showed that the use of a N₂-saturated atmosphere reduced the loss of functional molecules, especially vitamin E, in both cultivars, during long storage periods. Moreover, the present system is suitable for the storage of seeds of old varieties cultivated under organic agriculture. Overall, the results validate the efficacy of the storage method with N₂ and suggest its possible use for wheat on an industrial scale.

Introduction

Cereals intended for either animal or human nutrition are prone to significant losses, both quantitatively and qualitatively, during long-term storage. This is attributable to a) abiotic factors, such as inadequate drying, high temperature and humidity, b) attacks of rodents and microorganisms (bacteria and fungi, including those producing mycotoxins) (Kumar and Kalita, 2017; Magan and Aldred, 2007). Although pesticides, such as phosphines (PH₃), are commonly used to protect the grains from these losses, the use of chemicals has significant negative implications, in particular on human health and the environment (Aulický and Stejskal, 2016).

The necessity of innovative agronomical practices capable of improving storage methods, ensuring food security and environmental sustainability, has stimulated the search for alternative strategies, among which the use of a controlled atmosphere (CA) (Banks and Annis, 1990; Subramanyam and Hagstrum, 2012).

In the last few decades, numerous studies have confirmed the validity of CA against pests, through the use of carbon dioxide (CO₂) and nitrogen (N₂) (Kumar and Kalita, 2017; Navarro, 2006; Navarro et al., 2012). Although both of these gases showed an improvement in grain quality, N₂ deserves a special consideration, as it is free of pollutants and thus environmental-friendly (Navarro et al., 2012; Ren et al., 2012).

The use of controlled (CA) or modified (MA) atmosphere is one of the most successful conservation techniques, which can be used for a wide variety of agricultural and food products, such as grains, meats, fruits and vegetables (Jayas and Jeyamkondan, 2002).

Several studies in the literature have described the combination of heat and CA for the preservation of stone fruits, such as cherries (Neven, 2005; Neven and Rehfield-Ray, 2006). The use of CA and modified atmosphere (MA) during packaging was also employed for the preservation of dried fruits and nuts, commodities which have a lower susceptibility to degradation (Miranda et al., 2019). Additionally, long-term storage in silos with CA (N₂) was reported to preserve the cereal quality of grains on a pilot scale already decades ago (Quaglia et al., 1980; Storey, 1980), as well as more recently in concrete silos (Iconomou et al., 2006). The storage method with N₂ [98.5 ± 0.5% (v/v)] described in this article was previously tested on a pilot scale on cereals, namely maize and wheat and was shown to hinder the growth of fungi, as well as the production of mycotoxins.

The technology used was based on the use of a membrane nitrogen separator (MNS) (Huiyi et al., 2012), resulting, on one hand, in a reduction of noxious agents (e.g. mycotoxins) without the use of chemical fumigants and, on the other, in the preservation of the nutraceutical components of the cereals during long-term storage.

In light of these results and considering the growing attention dedicated to the nutritional qualities of food and the relationship between consumption and human health, the use of CA with N₂ for the long-term storage of wheat was considered ideal to better preserve the contents of bioactive molecules. As well documented, wheat contains metabolites with antioxidant potential, represented by polyphenols, flavonoids and vitamins (Engelsen and Hansen, 2009; Žilić, 2016).

In recent years particular interest has also been centered around ancient wheat varieties, as well as old heritage varieties for beneficial health properties attributable to functional compounds (Dinu et al., 2017). It is generally accepted that ancient wheat has remained unchanged over the last hundred years, whereas modern species have been extensively modified and subject to cross-breeding in what is commonly referred to as the “Green Revolution”, in order to develop high-yielding varieties with improved storage protein quality and technological properties (Dinu et al., 2017). Senatore Cappelli (Triticum durum L.) and Verna (Triticum aestivum L.) are representative of old Italian heritage varieties. The consumption of products made with Cappelli (Ghiselli et al., 2013) and Verna (Sereni et al., 2017; Sofi et al., 2010) was shown to ameliorate not only pro-inflammatory/anti-oxidant parameters (where investigated), but also glycaemic and lipid status. The same effects were not evident after the consumption of products made from commercially available modern varieties (Ghiselli et al., 2013; Sereni et al., 2017; Sofi et al., 2010). In particular, Verna, aside from a significant beneficial effect on total cholesterol, LDL-cholesterol, as well as for blood glucose stimulated an increase in circulating endothelial progenitor cells (Sereni et al., 2017). Although both Verna and Cappelli were shown to have a greater diversity of phenolic molecules in comparison to the commercial modern counterparts (Dinelli et al., 2011), the actual contents of bioactive components in ancient and heritage varieties differ little from modern wheat species (Shewry and Hey, 2015), indicating that functional efficacy is evident from synergistic effects between combinations of various breakdown components.

Old cultivars benefit from unique morphological and molecular features, rendering these varieties more tolerant to pests, diseases and abiotic stress compared to commercial varieties (Berni et al., 2019, 2018; Cheng, 2018). Because of the growing interest in the cultivation of old cultivars in several Italian regions, such as Tuscany, this study is focused on two different old wheat cultivars that are largely commercialized, namely the above-mentioned Cappelli and Verna.

The long-term storage in silos at low temperatures was previously shown to have no major effects on the content of polyphenols and the anti-radical activity of commodities (Zhou et al., 2014). However, the storage in silos affects the preservation of the physico-chemical properties of lipids (Fastnaught et al., 2006; Galliard, 1986) by promoting oxidation. Considering that vitamin E shows a progressive decrease in content that is proportional with the increase in lipid oxidation (Chun et al., 2005), we here sought to investigate whether the use of CA (with N₂) could slow down the loss of vitamin E in the grains of the two old varieties.

This study paves the way to an innovative and eco-sustainable approach improving the storage of cereals and better preserving their nutritional value.