FERMENTATION EFFECT

CHANGES IN ANTIOXIDANT PROPERTIES OF CERTAIN PLANT-BASED FOODS THROUGH FERMENTATION

During fermentation, numerous biochemical processes occur in the structure of foods, and as a result, various properties of the product such as bioactivity and digestibility change. The structural changes that occur in phytochemicals through fermentation increase the phenolic content of foods, and accordingly, antioxidant activity increases. Many studies on this subject indicate that fermentation increases or does not negatively affect the capacity of antioxidants required for eliminating free radicals present in cells and foods. Within the scope of this study, the effect of fermentation – a method used to preserve and alter the nutritional and sensory properties of foods and to extend product shelf life – on the antioxidant capacities of certain plant-based foods has been examined.

1. Introduction

Phytochemicals naturally present in plant-based foods are generally in bound form, and their bioavailability is lower compared to phytochemicals in free form. For this reason, it has been aimed to increase the nutritional values of plant-based foods through bio-processes such as fermentation [1]. Fermentation is a method used to preserve and alter the nutritional and sensory properties of foods and to extend product shelf life [2]. During fermentation, numerous biochemical processes occur, including changes in the composition of foods, and the properties of the product such as bioactivity and digestibility are affected [3]. Furthermore, along with changes that occur in the bioactive compounds of the plant through fermentation, changes also take place in the texture and sensory properties of the food [1]. During fermentation, many enzymes that metabolize carbohydrates hydrolyze phenolic glycosides and release free aglycones with high antioxidant activity [4]. Additionally, through the effect of fermentation, the cell wall of cereals breaks down and the release or synthesis of various bioactive compounds occurs [5]. Another mechanism explaining the increase in antioxidant properties of plant products following fermentation is explained by structural changes in phytochemicals [6]. An increase is also observed in the phenolic content of foods after fermentation, and accordingly, antioxidant activity increases [7]. For all these reasons, whether fermentation can be one of the methods to develop the antioxidant activity of food substances is being debated. Antioxidant activity refers to the total capacity of antioxidants required to eliminate free radicals present in cells and foods. Food-derived antioxidants include vitamin C, tocopherols, carotenoids, lipoic acid, and various phytonutrients commonly found in plants [9]. Phenolic compounds exhibit high reducing agent properties, hydrogen transfer, and singlet oxygen binding capacity due to the 3'-4' dihydroxy group present in benzene rings [10]. Similarly, flavonoids also exhibit the ability to effectively eliminate hydroxyl and peroxyl radicals, form complexes with metals, and prevent lipid oxidation due to galloyl ester groups in the C (pyrene) rings. The antioxidant effects of tocopherols stem from their hydrogen atom transfer, singlet oxygen scavenging, and other reactive species scavenging effects. On the other hand, ascorbic acid is a very good electron donor with low electron reduction potential. The antioxidant mechanism of ascorbic acid stems from its hydrogen transfer to lipid radicals, singlet oxygen binding, and molecular oxygen elimination properties [11]. Within the scope of this study, the effect of fermentation on the antioxidant properties of various plant-based foods has been examined.

2. Changes in Antioxidant Properties of Certain Plant-Based Foods

Fruits and vegetables are food products rich in antioxidative compounds whose effects in preventing various chronic diseases such as cancer, cardiovascular disease, and diabetes have been demonstrated. Studies show that fermentation is one of the applicable methods to enhance the antioxidant properties of fruits and vegetables. In this context, there are various studies examining the changes in antioxidant properties through fermentation of foods such as apple pomace, ginseng, strawberry, olive, rosehip, blueberry, grape, and cabbage (Table 1). In a study in which ginseng seed was fermented with Bacillus subtilis, Lactobacillus gasseri, and Pediococcus pentosaceus in a batch system at 30°C for 24 hours, the antioxidant activity of the samples was determined using the ABTS 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) and superoxide dismutase (SOD) enzyme activity methods. It was found that fermented ginseng samples had higher antioxidant activity compared to unfermented products.

Additionally, samples fermented with B. subtilis showed higher ABTS radical scavenging activity compared to samples fermented with L. gasseri and P. pentosaceus; while SOD enzyme activity was found to be higher in samples fermented with L. gasseri and P. pentosaceus [12].

Following solid-state fermentation of apple pomace with Phanerocheate chrysosporium, the amount of phenolic matter increased from 4.6 mg (gallic acid equivalent) GAE/g to 16.12 mg GAE/g dry weight, and accordingly, phenolic extracts obtained from fermented apple pomace were found to have higher DPPH (2, 2-diphenyl-1-picrylhydrazyl) radical scavenging properties [13]. In a study where gluconic acid fermentation was applied, the suitability of strawberry for fermented diabetic beverage production was investigated using Gluconobacter japonicus. Through gluconic acid fermentation, glucose present in the strawberry structure was converted to gluconic acid. The antioxidant properties of unfermented strawberry and fermented product were compared using ORAC and DPPH methods. According to the findings obtained, it was concluded that there was no change in the antioxidant properties of the product obtained through fermentation, the antioxidant properties of the product were preserved, and gluconic acid fermentation was suitable for producing fermented beverages from strawberry [14]. In natural and controlled fermentation of olive with Lactobacillus plantarum, a reduction of 32-58% was observed in the total phenolic content of olive and 50-72% reduction in ABTS radical scavenging activity. Additionally, it was determined that olives obtained through controlled fermentation had higher antioxidant activity compared to olives produced through natural fermentation [6]. In another study, three different fermented cabbages were produced from white cabbage using L. plantarum, Leuconostoc mesenteroides, and a 1:1 mixture of these two microorganisms. After fermentation, the ORAC values of the obtained fermented cabbages increased 2-fold compared to unfermented cabbage.

The highest ORAC value was determined as 164 mmol Trolox/g dry weight in the fermented cabbage sample with L. mesenteroides [15]. As with fruits and vegetables, studies have confirmed that the antioxidant properties of grain and legume products also change through fermentation.

For example, there are various studies examining the changes in antioxidant properties through fermentation of foods such as soy, chickpea, rapeseed, wheat, barley, rye, and millet (Table 1). Following 24-hour batch fermentation of soybean with B. subtilis, the DPPH and superoxide radical scavenging activity of the obtained product increased 3.1 and 24-fold, respectively, compared to unfermented soybean. This has been attributed to the increase in free phenolic and amino acid amounts as a result of higher protein hydrolysis degrees in soybean during fermentation [16]. Similarly, in a study examining solid-phase fermentation of black soybean with B. subtilis, it was determined that products obtained through fermentation had higher antioxidant activity compared to unfermented samples. Additionally, while samples extracted with water showed the highest DPPH radical scavenging activity and iron chelating effect in unfermented black soybean; after fermentation, the highest DPPH radical scavenging effect and iron chelating effect were observed in samples extracted with acetone and methanol [17].

Following 24-hour batch fermentation of soy protein with L. plantarum, the ABTS radical scavenging activity, iron (III) reducing antioxidant power (FRAP), and hydroxyl and superoxide radical reducing capacity of the obtained product were found to be higher compared to unfermented soy protein [18].

Following solid-state fermentation of chickpea with Cordyceps militaris, it was found to exhibit higher DPPH radical scavenging activity compared to unfermented chickpea. DPPH radical scavenging activity in unfermented chickpea samples was 21.7% in methanol extraction, 21.7% in ethanol extraction, 17.7% in water extraction; while in fermented chickpea these values were 76.4%, 71.8%, and 30.8%, respectively. Similarly, ABTS radical scavenging activity and FRAP values were also found to be higher in fermented chickpea compared to unfermented chickpea [19]. For the purpose of peptide production with antioxidant properties, rapeseed was subjected to solid-state fermentation with B. subtilis at 32°C and 85% absolute humidity for 6 days. On day 2 of fermentation, a rapid increase was observed in the amount of peptides in rapeseed. The peptides obtained following fermentation were found to have high DPPH free radical scavenging activity, iron binding capacity, and lipid peroxidation prevention activities depending on concentration [20]. On the other hand, to determine the effect of fermentation on the antioxidant properties of buckwheat, wheat, barley, and rye, 24-hour batch fermentation was performed with Lactobacillus rhamnosus and S. cerevisiae. At the end of the fermentation process, cereals fermented with L. rhamnosus were found to have higher DPPH radical scavenging activity and FRAP values compared to cereals fermented with S. cerevisiae; and it was concluded that buckwheat was the cereal with the highest antioxidant capacity [21].

Table 1. Changes in antioxidant activity of certain plant-based foods through fermentation

3. Conclusion

Fermentation is one of the applicable methods to enhance the antioxidant properties of foods. When reviewing current studies, it is evident that many factors are effective on the antioxidant properties of fruits and vegetables as well as grain and legume products: the raw material used in fermentation, the initial antioxidant capacity of the raw material, the type of microorganism used for fermentation, fermentation conditions, the solvent used in extraction, and the method used in antioxidant activity determination. Future studies will be useful in monitoring the changes occurring in the antioxidant properties of different foods through fermentation, and in elucidating the mechanism by which fermentation increases antioxidant capacity. Research Assistant Gülay Özkan Istanbul Technical University Faculty of Chemistry and Metallurgy Department of Food Engineering     Associate Professor Funda Karbancıoğlu Güler Istanbul Technical University Faculty of Chemistry and Metallurgy Department of Food Engineering     Associate Professor Esra Çapanoğlu Güven Istanbul Technical University Faculty of Chemistry and Metallurgy Department of Food Engineering    

References [1] Yeo, S., & Ewe, J. (2015). Effect of fermentation on the phytochemical contents and antioxidant properties of plant foods. Advances in Fermented Foods and Beverages , 107–122. [2] Frias, J., Miranda, M. L., Doblado, R., & Vidal-Valverde, C. (2005). Effect of germination and fermentation on the antioxidant vitamin content and antioxidant capacity of Lupinus albus L. var. Multolupa. Food Chemistry , 92 (2), 211-220. [3] Zhang, Z., Lv, G., Pan, H., Fan, L., Soccol, C. R., & Pandey, A. (2012). Production of powerful antioxidant supplements via solid-state fermentatin of wheat (Triticum aestivum Linn.) by cordyceps militaris. Food Technology and Bİotechnology , 50 (1), 32-39. [4] Vattem, D. A., & Shetty, K. (2003). Ellagic acid production and phenolic antioxidant activity in cranberry pomace (Vaccinium macrocarpon) mediated by Lentinus edodes using a solid-state system. Process Biochemistry , 39 (3), 367–379. [5] Katina, K., Laitila, A., Juvonen, R., Liukkonen, K. H., Kariluoto, S., Piironen, V., et al. (2007). Bran fermentation as a means to enhance technological properties and bioactivity of rye. Food Microbiology , 24 (2), 175–186. [6] Othman, N. B., Roblain, D., Chammen, N., Thonart, P., & Hamdi, M. (2009). Antioxidant phenolic compounds loss during the fermentation of Chétoui olives. Food Chemistry , 116 (3), 662–669. [7] Ng, C., Wang, C., Wang, Y., Tzeng, W., & Shyu, Y. (2011). Lactic acid bacterial fermentation on the production of functional antioxidant herbal Anoectochilus formosanus Hayata. Journal of Bioscience and Bioengineering , 111 (3), 289–293. [8] Vecchia, C., Altieri, A., & Tavani, A. (2001). Vegetables, fruit , antioxidants and cancer: A Review of Italian Studies. European Journal of Nutrition , 40, 261-267. [9] Miller, N., & Rice-Evans, C. (1997). Factors influencing the antioxidant activity determined by the ABTS'+ radical cation assay. Free Radical Research , 26 (3), 195–199. [10] Lee, J., Koo, N., & Min, D. (2004). Reactive oxygen species, aging, and antioxidative nutraceuticals. Comprehensive Reviews in Food Science and Food Safety , 3 (1), 21-33. [11] Lee, M., Lee, Y., Kim, S., Hong, H., & Kim, H. (2015). Quality and antioxidant activity of ginseng seed processed by fermentation strains. Journal of Ginseng Research , 39, 178-182. [12] Ajila, C., Brar, S., Verma, M., Tyagi, R., & Valéro, J. (2011). Solid-state fermentation of apple pomace using Phanerocheate chrysosporium – Liberation and extraction of phenolic antioxidants. Food Chemistry , 126, 1071–1080. [13] Álvarez-Fernández, M., Hornedo-Ortega, R., & Cerezo, A. (2014). Non-anthocyanin phenolic compounds and antioxidant activity of beverages obtained by gluconic fermentation of strawberry. Innovative Food Science and Emerging Technologies , 26. [14] Martinez-Villaluenga, C., Peñas, E., Sidro, B., Ullate, M., Frías, J., & Vidal-Valverde, C. (2012). White cabbage fermentation improves ascorbigen content, antioxidant and nitric oxide production inhibitory activity in LPS-induced macrophages. LWT-Food Science and Technology, 46(1), 77-83. [15] Sanjukta, S., Rai, A., Muhammed, A., Jeyaram, K., & Talukdar, N. (2015). Enhancement of antioxidant properties of two soybean varieties of Sikkim Himalayan region by proteolytic Bacillus subtilis fermentation. Journal of Functional Foods , 14, 650–658. [16] Juan, M., & Chou, C. (2010). Enhancement of antioxidant activity, total phenolic and flavonoid content of black soybeans by solid state fermentation with Bacillus subtilis BCRC 14715. Food Microbiology , 27, 586-591. [17] Xiao, Y., Wang, L., Rui, X., Li, W., Chen, X., Jiang, M., et al. (2015). Enhancement of the antioxidant capacity of soy whey by fermentation with Lactobacillus plantarum B1–6. Journal of Functional Foods , 12, 33–44. [18] Xiao, Y., Xing, G., Rui, X., Li, W., Chen, X., & Jiang, M. (2014). Enhancement of the antioxidant capacity of chickpeas by solid state fermentation with Cordyceps militaris SN-18. Journal of Functional Foods , 10, 210–222. [19] He, R., Ju, X., Yuan, J., Wang, L., Girgih, A., & Aluko, R. (2012). Antioxidant activities of rapeseed peptides produced by solid state fermentation. Food Research International , 40, 432–438. [20] Dordevic, T., Siiler-Marinkovic, S., & Dimitrijevic-Brankovic, S. (2010). Effect of fermentation on antioxidant properties of some cereals and pseudo cereals. Food Chemistry , 119, 957–963.