Xylanase Production by Solid-State Fermentation for the Extraction of Xylooligosaccharides from Soybean Hulls§.

Research background: The development of a novel process for the production of xylooligosaccharides (XOS) based on the 4R concept is made possible by the integration of numerous techniques, especially enzymatic modification together with the physical pretreatment of renewable materials. This study aims to integrate the use of agricultural wastes for the production of xylanase by a new strain of Penicillium sp. and value-added products, XOS. Experimental approach: For the production of xylanase, a solid-state fermentation was performed using wheat bran as substrate. To obtain the most active crude extract of xylanase, the time frame of cultivation was first adjusted. Then, the downstream process for xylanase purification was developed by combining different membrane separation units with size exclusion chromatography. Further characterisation included determination of the optimal pH and temperature, determination of the molecular mass of the purified xylanase and analysis of kinetic parameters. Subsequently, the hydrolytic ability of the partially purified xylanase in the hydrolysis of alkali-extracted hemicellulose from soybean hulls was investigated. Results and conclusions: Our results show that Penicillium rubens produced extracellular xylanase at a yield of 21 U/g during solid-state fermentation. Using two ultrafiltration membranes of 10 and 3 kDa in combination with size exclusion chromatography, a yield of 49 % and 13-fold purification of xylanase was achieved. The purified xylanase (35 kDa) cleaved linear bonds ß-(1→4) in beechwood xylan at a maximum rate of 0.64 µmol/(min·mg) and a Michaelis constant of 44 mg/mL. At pH=6 and 45 °C, the purified xylanase showed its maximum activity. The xylanase produced showed a high ability to hydrolyse the hemicellulose fraction isolated from soybean hulls, as confirmed by thin-layer chromatography. In the hydrothermally pretreated hemicellulose hydrolysate, the content of XOS with different degrees of polymerisation was detected, while in the non-pretreated hemicellulose hydrolysate, the content of xylotriose and glucose was confirmed. Novelty and scientific contribution: Future research focusing on the creation of new enzymatic pathways for use in processes to convert renewable materials into value-added products can draw on our findings.

Oat protein concentrate as alternative ingredient for non-dairy yoghurt-type product.

BACKGROUND: During the industrial production of ß-glucan, a protein-rich fraction remains as a by-product. Recovery of this protein as oat protein concentrate (OPC) results in a source of cereal protein for food and improves the overall economy of the process. In this study, a yoghurt-type product is developed by lactic acid fermentation of an OPC suspension after subjection to heat treatment to assure starch gelatinization. RESULTS: In detail, the process of yoghurt production involved an initial heating step to 90 °C, followed by 24 h fermentation with a starter culture consisting of Lactobacillus delbrueckii subsp. bulgaricus und Streptococcus thermophilus. The resulting yoghurt-type product was mildly sour (pH 4.2) with a certain amount of lactic acid (3.3 ± 0.2 g kg-1 ) and contained 4.9 × 106 cfu g-1 lactobacillus after 24 h fermentation. Scanning electron microscopy revealed a porous network presumably built up from the gelatinized starch fraction containing aggregated structures, between which were assumed to be aggregated oat proteins. Moreover, to a limited extent, proteolysis occurred during fermentation. Thus some of the proteolytic enzymes present in the yoghurt culture cleaved oat protein and released peptides. However, the effect on essential amino acids was small. CONCLUSION: The results of this study provide a deeper knowledge into the role of starch and protein in fermented OPC yoghurts. The structure of fermented OPC verifies the applicability of oat protein as an alternative source for yoghurt-type products. © 2019 Society of Chemical Industry.

Sensory and physicochemical changes in gluten-free oat biscuits stored under different packaging and light conditions.

The influence of different packaging films and their thickness (polyethylene terephthalate/casting polypropylene (PET/CPP_34), biaxially oriented polypropylene (BOPP_40), polyvinylchloride (PVC_12), BOPP/CPP_50 and polyethylene/ethylene vinyl alcohol/polypropylene (PE/EVOH/PP_50) on the quality of gluten-free oat biscuits was evaluated for a storage period up to 3 months under light and darkness conditions. Periodically (day 30, 60 and 90), physical parameters, peroxide value, texture and microbiological parameters together with sensory attributes (surface colour, smell, taste, crunchiness and off-flavour) were assessed. Moisture and water activity of biscuits decreased during storage in all packages. The highest peroxide value was obtained for biscuits packed in PVC_12, while the lowest was for the PE/EVOH/PP_50, for both storage conditions. The biscuits' colour changed from yellow-brown to light yellow and the change was more pronounced in the light as compared to the dark storage conditions. The hardness value decreased (p > 0.05) during the storage period. The electronic nose system showed that the distinct volatile composition of the biscuits stored in the light was correlated with the higher scores of the off-flavour attribute and with the peroxide values. The sensory data showed that BOPP/CPP_50 preserved the colour of the biscuits, while PE/EVOH/PP_50 kept the initial crunchiness of the biscuits up to 90 days of storage in both light and dark conditions. The study suggested that BOPP/CPP_50 and PE/EVOH/PP_50 can be used for gluten-free oat biscuits' packaging and storage up to 90 days for both conditions studied, without adversely affecting their physicochemical and sensory properties.

Impact of Different Enzymatic Processes on Antioxidant, Nutritional and Functional Properties of Soy Protein Hydrolysates Incorporated into Novel Cookies.

Soy protein concentrate (SPC) was hydrolyzed using several commercial food-grade proteases (Alcalase, Neutrase, papain, Everlase, Umamizyme, Flavourzyme) and their combination to obtain promising ingredients in the manufacture of functional bakery products. In all cases, the hydrolysis caused nutritional, sensory, and rheological changes in SPC, as well as protein structural changes like increased surface hydrophobicity and content of exposed SH groups with the magnitude of these changes depending on enzyme specificity. The hydrolysis with the combination of Neutrase and Flavourzyme (NeuFlav) increased essential amino acid content by 9.8% and that of Lys by 32.6% compared to SPC. This hydrolysate showed also significant antioxidant activities including ABTS and superoxide anion scavenging activity and metal-chelating ability. The addition of all hydrolysates in wheat flour decreased water adsorption and increased development time to some extent due to gluten network weakening, but also decreased the rate of starch retrogradation, contributing to the increase of the shelf-life of bakery products. The NeuFlav tasted less bitter than other hydrolysates, while E-nose provided a discrimination index of 93 between control and hydrolysates. It appeared that the addition of the NeuFlav hydrolysate in a cookie formulation improved protein content and nutritional quality and directed to its higher general consumer acceptability than cookies formulated with only wheat flour.

The Role of Hydrocolloids in Gluten-Free Bread and Pasta; Rheology, Characteristics, Staling and Glycemic Index.

Hydrocolloids are important ingredients controlling the quality characteristics of the final bakery products. Hydrocolloids are frequently used in gluten-free (GF) recipes, mimicking some rheological properties of gluten, improving dough properties, delaying starch retrogradation and improving bread texture, appearance and stability. Hydrocolloids addition increases viscosity and incorporation of air into the GF dough/batter. Besides their advantages for the technological properties of the GF bread, hydrocolloids addition may impact the glycemic index (GI) of the final product, thus answering the demand of people requiring products with low GI. This review deals with the application of hydrocolloids in GF bread and pasta with a focus on their effect on dough rheology, bread hardness, specific volume, staling and GI.

Evaluation of the storage-associated changes in the fatty acid profile of oat-based gluten-free cookies prepared with different fats.

This study was carried out to investigate storage-associated changes in the fatty acid profile (with GC and 1H-NMR techniques) of oat-based gluten-free cookies prepared with different fats: margarine (MAR), butter (BUT), lard (LAR), refined palm oil (RPO), refined palm oil with stearin (RPOS), and hydrogenated palm oil (HPO). GC analysis indicated that palmitic and stearic acid were the predominant saturated fatty acids (SFAs), regardless of the type of fat used. cis-Oleic acid represented the major monounsaturated fatty acid (MUFA), while cis-linoleic acid was the most abundant polyunsaturated fatty acid (PUFA). After 6 months of storage, a significant decreasing trend in SFA concentration was observed for LAR and RPOS cookies, while a decrease in MUFA concentration was observed only for HPO cookies. In fresh cookies and in cookies stored for 6 months, the contents of SFA, MUFA, and PUFA determined by GC were positively correlated with those determined by 1H-NMR (r > 0.90).

Effect of theanine and polyphenols enriched fractions from decaffeinated tea dust on the formation of Maillard reaction products and sensory attributes of breads.

The antiglycoxidative properties of theanine (TEF) and polyphenols enriched fractions (PEF) prepared from tea dust were tested in a model system composed of bovine serum albumin (BSA) and methylglyoxal (MGO). PEF caused a decrease in available free amino groups of BSA in presence and absence of MGO, suggesting the simultaneous occurrence of glycoxidation reaction and phenols-protein interaction. The presence of PEF and TEF inhibited formation of fluorescent advanced glycation end-products (AGEs). Moreover, theanine (TB) and polyphenol-enriched bread (PB) were formulated. A significant increase in free amino groups was observed in TBs with a dose-response effect, while addition of PEF in bread produced a significant decrease (p<0.05). PEF efficiently reduced fluorescent AGE formation in breads compared with TEF. The results are in line with the simplified model systems. PEF used as food ingredient allows obtaining a tasty food possessing health promoting properties and lower content of potential harmful compounds (AGEs).