Solid-state fermentation of canola meal with Aspergillus sojae, Aspergillus ficuum and their co-cultures: Effects on physicochemical, microbiological and functional properties

Highlights

• Canola meal was fermented with food grade Aspergillus fungi.

• Phytic acid content and total glucosinolates decreased during solid-state fermentation.

• Microbiological counts of canola meal increased during solid-state fermentation.

• Changes in protein band intensity during solid-state fermentation were demonstrated.

• Solid-state fermented canola meal is a promising food product and functional ingredient.

Abstract

Effects of solid-state fermentation (SSF) with Aspergillus sojae, Aspergillus ficuum and their co-cultures on physicochemical, microbiological and functional properties of canola meal (CM) were investigated. Fibre fractions, in vitro enzyme protein digestion, protein molecular distribution and colour attributes were also evaluated. Samples did not differ in their proximate composition except in soluble carbohydrate (glucose) and starch. The microbiological counts of the fermented meals were higher than that of the unfermented CM. Phytic acid content and total glucosinolates reduced (p < 0.05) in the fermented meals. SSF reduced the protein molecular weight of CM, colour attributes, but increased water absorption capacity, swelling index and swelling capacity. Therefore, the study indicated that SSF of CM with A. sojae, A. ficuum and their co-cultures can improve the physicochemical, microbiological and functional properties of CM. Solid-state fermented CM is a promising ingredient and can find potential industrial applications in the development of novel nutritious food and feed products.

Introduction

Canola meal (CM) is an important feedstuff derived during the extraction of oil from canola seeds. It has high nutritional quality because it contains about 36.13% crude protein, 11.54% crude fibre (Khattab & Arntfield, 2009), methionine, cysteine and moderate source of essential minerals. Presently, CM is only second to soybean meal as the most commonly used protein feedstuff in animal diets around the world (Newkirk, 2009). However, the continuous growth in human population keeps increasing the demand for dietary protein and it is projected that CM will shift from being an animal feed resource to a common ingredient in many food products so as to meet future protein requirements (Olukomaiya, Fernando, Mereddy, Li, & Sultanbawa, 2019c). Despite its unique composition, the anti-nutritional factors (ANFs) in CM such as fibre, tannins, phytic acid and other ANFs have been reported to reduce performance of non-ruminant animals when fed at high inclusion levels (Meng & Slominski, 2005). CM contains less than 10 μmol/g total glucosinolates (Rogiewicz & Slominski, 2019), 1.5–3.0% tannins, 0.6–1.8% sinapine and 3.0–6.0% phytic acid (Bell, 1993). Dietary fibre may have functional properties (Buttriss & Stokes, 2008), but cannot be digested by the endogenous enzymes of non-ruminant animals. The fibre in CM can also inhibit the absorption of other nutrients such as protein and minerals (Grieshop, Reese, & Fahey, 2001). The fairly high fibre content in CM, thus, reduces the energy density of diets and compromises performance (Zhou, Oryschak, Zijlstra, & Beltranena, 2013). Processing strategies to improve the nutritive quality of CM for food and feed purposes have been ongoing for decades, and treatments with heat (Newkirk & Classen, 2002), organic solvents (Kozlowska, 1986), addition of enzymes (Jensen, Olsen, & Sorensen, 1990), roasting and water boiling (Khattab & Arntfield, 2009) have been reported. However, the drawbacks of some of the strategies include inability to thoroughly eliminate ANFs, protein loss and cost/commercial unfeasibility. Solid-state fermentation (SSF) as a processing technique has been researched for many years in the food and fermentation industries (Nair & Duvnjak, 1991; Aljuobori, Idrus, Soleimani, Abdullah, & Juan Boo, 2017; Olukomaiya, Fernando, Mereddy, Li, & Sultanbawa, 2019b; Olukomaiya, Fernando, Mereddy, Li, & Sultanbawa, 2019 c). SSF has huge potential for obtaining bioactive compounds; since, microorganisms such as fungi can naturally synthesize enzymes that break down the cell wall thereby generating a hydrolysis and mobilization of compounds towards the extraction solvent (Jamal, Idris, & Alam, 2011; Martínez-Ávila, Aguilera-Carbó, Rodríguez-Herrera, & Aguilar, 2012; Torres-León et al., 2019). In recent times, SSF is performed at a commercial scale in the food industry or in waste treatment and utilization. The beneficial effect of SSF in enhancing the nutritive value and bioactivity of other oilseed meals such as rapeseed meal (Hu et al., 2016), soybean meal (Li et al., 2019) and cottonseed meal (Sun et al., 2013) using different microorganisms have been previously reported. It has also been reported that fermentation of CM with Lactobacillus salivarius (Aljuobori, Idrus, Soleimani, Abdullah, and Juan Boo (2017) and Saccharomyces cerevisiae (Olukomaiya et al., 2019a; Plaipetch & Yakupitiyage, 2014) improved the nutritional quality and reduced the levels of ANFs prior to inclusion in animal feeds. Aspergillus strains of Aspergillus sojae and Aspergillus ficuum have been certified as safe with regards to their epidemiological features and GRAS (Generally Regarded as Safe) status in the food industry (Gurkok, Cekmecelioglu, & Ogel, 2011; Heerd, Yegin, Tari, & Fernandez-Lahore, 2012; Shin, Kim, Lee, & Lim, 2019). Aspergillus sojae is a filamentous fungus which possesses the ability to secrete a wide range of hydrolytic enzymes such as amylase, protease, xylanase, etc that can hydrolyze complex compounds into simple ones (Szendefy, Szakacs, & Christopher, 2006; Wang, Ridgway, Gu, & Moo-Young, 2005). It is widely used in Japan for soybean fermentation and in producing traditional Japanese soy sauce (shoyu), soy paste and koji (Kim, Lim, Lee, Hurrh, & Lee, 2017; Machida et al., 2005). Aspergillus ficuum can be regarded as the highest producer of active phytase (Ullah, 1988; Ullah & Phillippy, 1994). A. ficuum can produce alpha-galactosidase and xylanase under SSF conditions (Lu et al., 2008; Shankar & Mulimani, 2007). Furthermore, A. sojae and A. ficuum have been used in producing phytase enzyme and degrading phytic acid content in different food and agro-industrial by-products (Chen, Vadlani, & Madl, 2014; Chen, Vadlani, Madl, & Gibbons, 2016; Nair & Duvnjak, 1991). Although studies have investigated the effect of SSF in improving the nutritional value and nutrient digestibility, decreasing ANFs and producing enzymes from CM (Aljuobori et al., 2017; Ebune, Al-Asheh, & Duvnjak, 1995; Nair & Duvnjak, 1991), there are needs for more information on other important aspects such as fibre fractions, microbiological properties, protein molecular distribution and functional properties as knowledge in these areas can enhance more commercial applications as functional food and feed ingredients. Therefore, the aim of the present study was to determine the effect of SSF with A. sojae, A. ficuum and their co-cultures on the physicochemical, microbiological and functional properties of canola meal.