Impact of a novel partial defatting technology on oxidative stability and sensory properties of peanut kernels
Introduction
Lipid oxidation has long been recognized as a substantial problem by the food industry, since oxidation affects shelf-life. In addition, high-fat diets as well as lipid peroxidation in foods are linked to health effects, such as obesity, premature aging, and increased risk of cancer and other diseases (Shebaby et al., 2015, Zalloua et al., 2019, Bassil and Obeid, 2016, Nasreddine et al., 2019). Recently, organoleptic and damage to membrane lipids in flax (Linum usitatissimum) during oxidation were elaborated in detail (Socrier et al., 2019). In fact, lipid oxidation also results in undesirable flavors and aromas, deterioration of nutrients and, even, generation of toxic compounds (Domínguez et al., 2019), which compromise the nutritional quality of fatty foods as well as shortening product shelf-life.
Fat content alone is not a good indicator of storage stability, but the degree of saturation (Socrier et al., 2019) and moisture content (Chen et al., 2017) are major factors that affect oxidative stability of foods. The extent of lipid oxidation can be measured using several methods including analysis of peroxide value and p-anisidine, which are indicative of primary and secondary oxidation products, respectively (Bañares et al., 2019). Assays determining thiobarbituric acid (TBA), oxiranes, aldehydes, conjugated dienes, and fluorescent compounds are just some of many other methods of analysis for lipid oxidation end-products (Domínguez et al., 2019). Sensory analyses also serve well to evaluate oxidation (Shakerardekani et al., 2013) and to detect any flavor, aroma, color, and texture alterations, mainly caused by the release of volatile compounds and the changes in lipid-protein interactions induced by oxidation of the lipid moiety (Kanner & Rosenthal, 1992).
Since peanuts contain 50 to 60% of lipids, of which approximately 80% are unsaturated fatty acids (Divino et al., 1996), they are highly susceptible to oxidation. In raw peanuts, oxidation of unsaturated fatty acids is mainly enzymatic and is triggered by a high lipoxygenase activity (Lin et al., 2019). Then, lipoxygenase is inactivated during reconstitution, and when peanuts are roasted, autoxidation takes place since high temperature treatments have a destructive effect on enzymes.
It is well established that fatty foods are vulnerable to oxidation, shortening shelf-life and compromising flavor and aroma, which impacts consumer acceptability. Conversely, consumer desire for high-fat foods is still high, despite the damaging health effects, meaning the industry is looking for methods that reduce fat content whilst protecting any remaining lipids for longer. In this respect, few studies on low-fat peanuts and their oxidative stability were reported in the literature (Nader & Louka, 2018). Most of the researchers agreed on the following widely supported hypothesis: the lower the lipid content of a defatted product, the less it is prone to oxidative rancidity. Thus, low-fat peanuts were thought to oxidize and develop off-flavors at a slower rate than full-fat counterpart. Inversely, Roozen et al. (1994a) revealed in their study that lowering the fat content of a food model could initiate oxidative deterioration and consequently increase flavor defects. The same authors (Roozen et al., 1994b) indicated that lipid concentration, type of lipids, and antioxidants are key factors affecting formation of volatile compounds.
In brief, the reaction of molecular oxygen with lipids has for long been a process of considerable interest, but oxidative changes in low-fat peanuts as affected by a mechanical defatting process was barely investigated in previous studies (Nader & Louka, 2018).
Accordingly, the current research has focused on some of the remarkable implications of lipid oxidative damages on peanut kernels further to different defatting treatments by a newly implemented technology called “mechanical expression preserving shape integrity” (MEPSI) (Louka and Nader, 2014, Louka et al., 2014, Nader and Louka, 2018). For this purpose, peanuts’ wholesomeness was controlled by following the deterioration of sensory properties (mainly flavor and aroma), as well as the decay of nutritional and food safety qualities relative to different combinations of process parameters. In this respect, Response Surface Methodology (RSM) was adopted for creating the experimental design, for process modeling, and for optimization of process parameters (water content, pressure, and processing duration) based on maximizing the sensory scores (for aroma [ARO] and taste [TAS]) and minimizing the extent of oxidation after treatment (lowest values of free fatty acid [FFA], peroxide value [PV], p-anisidine value [AV], and total oxidation [TotOx]).
Section snippets
Samples
Raw peanuts of Chinese origin (10 kg; Laixi city shunxiang peanuts product's Co. LTD, Qingdao, China), previously dried to 5.56 ± 0.24% d.b. water content, were procured from El Kazzi (Beirut, Lebanon).
Experimental setup
The experimental setup for defatting has been described in detail elsewhere (Nader et al., 2016a) and was used with an innovative modification aimed at enhancing efficiency and restoring peanut shape after defatting (Nader & Louka, 2018). As a result, peanuts were defatted using MEPSI, minimizing
Response values of the experimental design
Table 1 shows the results of oil extraction yields (i.e. Defatting Ratio [DR]) and percentage of irreversible deformations (i.e., Unrecoverable Deformation Ratio [UDR]) along with chemical ([FFA], [PV], [AV], [TotOx]) and sensory ([TAS] and [ARO]) response parameters for the 20 experiments. In fact, a detailed analysis of DR and UDR variation in function of MEPSI process parameters ([W], [P], and [t]) was previously carried out by Nader et al. (2016a). Nevertheless, DR and UDR results were
Conclusion
MEPSI technology showed its effectiveness as an eco-friendly defatting process while being less energy consuming than prior art technologies. The novelty of this method relies on the production of lower in calorie peanuts while limiting the structural damages during defatting and preserving the sensory properties of the finished roasted product. However, the current study showed that partial defatting of peanuts is prominently associated with higher risk of lipid oxidation and flavor
Perspective
It is worth mentioning that shelf-life of partially defatted peanuts can be extended by several further methods: (i) use of high-oleic peanuts rather than normal oleic ones since the former were proven to have higher levels of antioxidants (Craft et al., 2010), ten times slower oxidation rate (Peterson, 2009), and longer shelf-life; and (ii) reduction in molecular oxygen from the system that can be accomplished by edible coatings to prevent both moisture loss and oxygen diffusion (Haq et al.,
CRediT authorship contribution statement
Joelle Nader: Conceptualization, Methodology, Software, Visualization, Formal analysis, Investigation, Writing - original draft, Writing - review & editing. Charbel Afif: Data curation, Resources, Supervision, Project administration. Nicolas Louka: Conceptualization, Validation, Investigation, Writing - review & editing, Funding acquisition.
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.
Acknowledgements
The authors gratefully acknowledge the Lebanese company “El-Kazzi” and the Council for Scientific Research of Saint Joseph University, Lebanon (Project FS34) for providing financial support to carry out this research work.
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