Effects of gastrointestinal digestion and heating on the allergenicity of the kiwi allergens Act d 1, actinidin, and Act d 2, a thaumatin-like protein

Kiwifruit is a significant elicitor of allergy both in children and adults. Digestibility of two kiwifruit allergens, actinidin (Act d 1) and thaumatin-like protein (Act d 2), was assessed using an in vitro digestion system that approximates physiological conditions with respect to the passage of food through the stomach into the duodenum. Act d 1 precipitated in simulated gastric fluid at pH 2 and digestion of the aggregated protein proceeded slowly. The residual precipitate redissolved completely in simulated duodenal fluid at pH 6.5 and was partially digested. Forty percent of Act d 2 remained intact during gastric digestion and were cleaved by duodenal proteases into large fragments covalently linked by disulfide bonds. Both digested allergen samples displayed nearly unchanged IgE binding abilities. Circular dichroism spectra were used to analyze heat and acid-induced unfolding. Thermal stability of both allergens was strongly pH dependent. While Act d 1 was irreversibly destabilized in acidic solutions, heat-induced denaturation of Act d 2 at pH 2 was fully reversible. IgE binding to Act d 2 but not Act d 1 was detected in processed food products. The stability of Act d 1 and Act d 2 provides one explanation for the allergenic potency of kiwifruit.     

Enhanced bactericidal action and masking of allergen structure of soy protein by attachment of chitosan through Maillard‐type protein‐polysaccharide conjugation

The soy protein‐chitosan conjugate was formed by the Maillard reaction in dry state (relative humidity 65%) at 60°C for 2 weeks to improve the functional properties. The antimicrobial activity of the Maillard‐type soy protein‐chitosan conjugates enhanced 2–3 times that of soy protein‐chitosan mixture. The soy protein‐chitosan conjugate showed excellent emulsifying property with the progress of Maillard‐type conjugation. The allergenicity of soy protein was greatly decreased by the attachment of chitosan through Maillard reaction. The immonoblotting analysis with patient's sera revealed that soy protein‐chitosan conjugate was more effective to mask the allergen structure of soy protein causing from 34 kDa‐protein (Gly m Bd 30K) than soy protein‐galactomannan conjugate. The Western blotting showed that allergen (34 kDa‐protein) was completely masked by soy protein‐chitosan conjugation, while it was not completely masked by soy protein‐galactomannan conjugation.     

Germin-like protein Cit s 1 and profilin Cit s 2 are major allergens in orange (Citrus sinensis) fruits

Oranges are clinically relevant allergenic foods. To date, orange allergens have not been characterized in detail. The study is aimed at analyzing the sensitization profile in orange-sensitized subjects with and without clinical allergy, and to identify orange allergens. Fifty-six sensitized subjects with self-reported reactions to orange were grouped into reactors (anaphylaxis or multiple episodes of immediate reactions and/or positive challenge tests) and non-reactors (negative open food challenge tests). Allergens were characterized by IgE immunoblotting, N-terminal sequencing, IgE-inhibition assays, and mediator release assays were performed to determine the allergenic potency of orange profilin. Of 56 subjects, 23 were classified as orange allergic showing mainly an oral allergy syndrome. Of 23 subjects classified as orange allergic, 22 were sensitized to profilin, Cit s 2. In patients with mono-sensitization to profilin in vitro histamine releases up to 75% from basophils were induced using orange extract and purified plant profilins. Of the allergic patients 78% were sensitized to germin-like protein, Cit s 1. Both allergens showed retained IgE reactivity in heat-processed orange juice. Interestingly, subjects with and without clinical allergy showed a comparable sensitization profile. Profilin and germin-like proteins are major orange allergens. The potential clinical relevance of orange profilin was indicated by its strong capacity to release histamine from basophils. However, a predominant sensitization to both allergens in subjects without symptoms also indicates a high frequency of clinically insignificant sensitization.     

Physicochemical and sensory characteristics of soya protein isolate hydrolysates with added substrate‐like amino acids

Soya protein isolate (SPI) with or without added substrate‐like amino acid was subject to enzymatic hydrolysis catalysed by commercial proteases (Alcalase 2.4 L, flavourzyme and pancreatin). Addition of a small amount of amino acids (amino acid: SPI = 1: 2500, mol g^?1) during hydrolysis would cause a significantly (P < 0.05) reduced protein recovery, increased degree of hydrolysis, and altered amino acid composition and antioxidant activities of SPI hydrolysates. The SPI hydrolysates prepared with added Asp, Arg or Lys exhibited a higher antioxidant activity than the control. The bitterness of SPI hydrolysates was largely reduced upon addition of Met, Asp or Glu during hydrolysis, whilst the umami taste and mouthfeel‐liking were remarkably increased. Therefore, adding amino acid during hydrolysis is a feasible and beneficial approach to improve both the functional and sensory properties of SPI hydrolysate.     

Processing of bottom‐fermented gluten‐free beer‐like beverages based on buckwheat and quinoa malt with chemical and sensory characterization

Typical beer contains significant amount of gluten, and being the third most popular beverage worldwide, the commercial production of its gluten‐free form is of rising interest. This research aimed to prepare bottom‐fermented beverages from buckwheat and quinoa and to explore their physical, chemical and sensory properties. Compared with barley, the analysis of brewing attributes of buckwheat and quinoa showed a lower malt extracts, longer saccharification times, higher total protein and fermentable amino nitrogen content and higher values of the iodine test and colour. Fermentability values, the wort pH and the soluble protein content were similar for barley and buckwheat, but different for quinoa, whereas only values of viscosity and beverage pH were similar between barley and quinoa. Both beverages, especially the quinoa beverage, contained a superior level of metal cations. The fermentable carbohydrate content in the buckwheat wort was comparable to barley but lower in quinoa; however, worts derived from both pseudocereals contained predominantly glucose. The amino acid content of the buckwheat wort was similar to barley, whereas the content in the quinoa beverage was almost twice as high. The content of volatile compounds commonly associated with beer aroma was comparable between the barley and buckwheat beverage but significantly lower in the quinoa; however, the latter contained some distinctive volatile substances not found in the other beverages. The organoleptic perception of the buckwheat beverage was better than that of the quinoa, although both showed a good general acceptance. In general, buckwheat appears quite similar to barley, whereas quinoa shows many unique properties. Copyright © 2014 The Institute of Brewing & Distilling     

A nondigestible saccharide,fructooligosaccharide, increases the promotive effect of a flavonoid, α‐glucosyl‐isoquercitrin,on glucagon‐like peptide 1 (GLP‐1) secretion in rat intestine and enteroendocrine cells

This study conducted in vivo and in situ experiments with rats to investigate the glucagon‐like peptide‐1 (GLP‐1) secretion in response to oral or ileal administration of α‐glucosyl‐isoquercitrin (20–40 mmol in 2 mL; Q3G), fructooligosaccharides (200 mmol in 2 mL; FOS) and Q3G + FOS. Direct effects on GLP‐1‐producing l ‐cells were also examined by an in vitro study using a murine enteroendocrine cell line, GLUTag. To evaluate the plasma GLP‐1 level, blood samples from jugular cannula for in vivo and portal cannula for in situ experiments were obtained before and after administration of Q3G, FOS, or Q3G + FOS. We found tendencies for increases but transient stimulation of GLP‐1 secretion by Q3G in in vivo and in situ experiments. Although FOS alone did not have any effects, Q3G + FOS enhanced and prolonged high plasma GLP‐1 level in both experiments. In addition, application of Q3G on GLUTag cells stimulated GLP‐1 secretion while FOS enhanced the effect of Q3G. Our results suggest that Q3G + FOS possess the potential for the management or prevention of Type 2 diabetes mellitus (T2DM) by enhancing and prolonging the GLP‐1 secretion via direct stimulation of GLP‐1 producing l ‐cell.     

Physiochemical,textural, sensory properties and probiotic survivability of Chinese Laosuan Nai (protein‐fortified set yoghurt) using polymerised whey protein as a co‐thickening agent

A new Chinese Laosuan Nai (protein‐fortified set yoghurt) was developed using polymerised whey protein (PWP, 0.4%, w/v) as a co‐thickening agent. The prototype was analysed for physiochemical, textural, sensory properties and probiotic survivability and compared with a commercial sample. Experimental yoghurts were significantly higher in pH, protein content, hardness and viscosity (P < 0.01). Microstructure indicated a uniform and denser protein network. Probiotics remained stable for Bifidobacterium during a 10‐week storage period. Results indicated that polymerised whey protein may be a novel protein‐based co‐thickening agent for making Chinese Laosuan Nai.