Controlled nitrogen atmosphere for the preservation of functional molecules during silos storage: A case study using old Italian wheat cultivars
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.
Section snippets
Sampling and storage of wheat
The wheat samples were collected directly from the producer (Terre Regionali Toscane company) in the area of Cernaia in Tuscany (Grosseto, Italy - GPS coordinates: 42° 47′27.8 ″N 11° 00′37.1″ E). Two different wheat cultivars were studied, Cappelli (T. durum) and Verna (T. aestivum), harvested at different time points, respectively, in June and July 2017. A prototype of laboratory-scale silos, present at the CRISBA-ISIS Research Center “Leopoldo II di Lorena” (Grosseto, Italy), was used. The
Polyphenol content and antiradical activity
The wheat samples were stored for a period of 18 months and sampled at 0, 3, 6, 12 and 18 months of storage in silos. The chemical assays (DPPH and F-D) were used to quantify and compare the free and bound molecules in wheat stored using the traditional method with those in the samples of interest preserved under CA.
Verna and Cappelli showed similar antiradical activities and polyphenol contents, which did not show statistically significant differences under CNTRL conditions and CA at the time
Discussion
The progressive loss of functional molecules during storage is one of the main factors impacting the nutritional properties of grains. Finding new methods preventing or slowing down this loss represents an important technological innovation in food science.
In this study, the content of functional molecules, namely polyphenols and vitamin E, were evaluated in two Italian old cultivars (i.e. Cappelli and Verna) stored in silos using traditional methods (use of PH3), as well as CA (N2).
Initially,
Funding
This work was funded by Eurosider S.a.s. di Ottavio Milli & C. and Fondazione Ente Cassa di Risparmio di Firenze.
CRediT authorship contribution statement
Lorenzo Moncini: Conceptualization, Methodology. Gabriele Simone: Investigation. Marco Romi: Conceptualization, Supervision, Project administration. Giampiero Cai: Supervision, Project administration. Gea Guerriero: Data curation, Writing - original draft. Anne Whittaker: Methodology, Investigation. Stefano Benedettelli: Data curation, Supervision. Roberto Berni: Conceptualization, Methodology, Investigation, Data curation.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
During the acquisition of the data, R.B. was in receipt of the PhD fellowship “Pegaso” financed by the Region Tuscany.
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