Effects of added whey protein aggregates on textural and microstructural properties of acidified milk model systems

Non-fat milk model systems containing 5% total protein were investigated with addition of micro- or nanoparticulated whey protein at two levels of casein (2.5% and 3.5%, w/w). The systems were subjected to homogenisation (20 MPa), heat treatment (90 °C for 5 min) and chemical (glucono-delta-lactone) acidification to pH 4.6 and characterised in terms of denaturation degree of whey protein, particle size, textural properties, rheology and microstructure. The model systems with nanoparticulated whey protein exhibited significant larger particle size after heating and provided acid gels with higher firmness and viscosity, faster gelation and lower syneresis and a denser microstructure. In contrast, microparticulated whey protein appeared to only weakly interact with other proteins present and resulted in a protein network with low connectivity in the resulting gels. Increasing the casein/whey protein ratio did not decrease the gel strength in the acidified milk model systems with added whey protein aggregates.     

Iron‐encapsulated cold‐set whey protein isolate gel powder – Part 1: Optimisation of preparation conditions and in vitro evaluation

A central composite design with a quadratic model was used to investigate the effects of three independent variables involved in the synthesis of iron‐encapsulated cold‐set whey protein isolate gel (WPI) on encapsulation efficiency (EE) and L*, a*, b* colour characteristics. The optimal conditions for maximum EE with minimum colour alteration were determined as 6.8% WPI, 18.8 mM iron and pH 7. In an in vitro gastrointestinal assay, only about 28% of the encapsulated iron was released in the gastric condition (with pepsin at pH 1.2), compared to 95% in the intestinal condition (with pancreatin at pH 7.5).     

Zinc‐loaded whey protein nanoparticles prepared by enzymatic cross‐linking and desolvation

Zinc‐loaded whey protein nanoparticles were prepared by enzymatic cross‐linking whey protein followed by ethanol desolvation. Whey protein isolate (WPI) was denatured by heating (80 °C for 15 min) at pH 7.0 and then cross‐linked by transglutaminase at 50 °C for 4 h while stirring. Transglutaminase was inactivated by heating at 90 °C for 10 min, and then, ZnSO₄·7H₂O (1–10 mm ) was added. Zinc‐loaded whey protein nanoparticles were formed by adding ethanol at one to five times the volume of the protein solution at pH 9.0. The desolvated solutions were diluted by adding distilled water at ratio of 1:100 (w/v) immediately after desolvation. Dynamic light scattering (DLS) data showed that the particle size of zinc‐loaded whey protein nanoparticles increased with the amount of zinc and the volume of ethanol. Scanning electron microscopy micrographs revealed an almost spherical morphology for zinc‐loaded whey protein nanoparticles. The zinc loading efficiency was determined ranging from 76.7% to 99.2%. In vitro test data showed that the zinc release rate was low in simulated gastric fluid but high in simulated intestinal fluid. The results indicated that enzymatic cross‐linked whey protein nanoparticles may be used as a good vehicle to deliver zinc as a supplement.     

Effects of particle size on physiochemical and in vitro digestion properties of durum wheat bran

In order to promote the potential health benefits of high fibre products, wheat bran is the main focus of the food industry. The physiochemical and in vitro digestion properties of wheat bran containing different particle size were investigated and compared against raw bran samples. Firstly, the bran sample containing superfine particles (11.63 μm) was hydrolyzed by the α-amylase, pepsin, and pancreatin enzymes separately using a single factor and orthogonal test. Secondly, optimized hydrolysis parameters of superfine particles were employed to measure in vitro digestibility of macronutrients in raw, coarse, medium, and superfine bran particles. The maximum degree of hydrolysis obtained via α-Amylase (concentration 10 mg mL⁻¹, pH 6.6, and time 12.5 min) was 55.71%; pepsin (concentration 50 mg mL⁻¹, pH 1.2, and time 9 h) was 82.10%; and pancreatin (concentration 100 mg mL⁻¹, pH 7.0 and time 12 h) was 84.71%, respectively. The highest in vitro digestibility rate of reducing sugar, protein, fat, and soluble fibre content was observed in superfine bran samples to 33.4%, 82.55%, 91.53%, and 21.66%, respectively.     

Changes in the phenolic contents and antioxidant activities of citrus peels from different cultivars after in vitro digestion

The aim of this study was to investigate the effects of in vitro digestion on the phenolic contents and antioxidant activities of citrus peels. Three different varieties of citrus peels (mandarin, ponkan and red tangerine) were treated with simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The results showed that the SGF or SIF treatments of the citrus peels did not significantly increase the total phenolic content (TPC) or total flavonoid content (TFC), except for that of the TFC of ponkan peel treated with SGF. However, simulated in vitro digestion did improve the antioxidant activities measured with FRAP and ABTS methods. The effect of SGF was more positive than those of SIF for the FRAP assay, but the opposite was true for ABTS. Notably, both simulated digestion techniques decreased the DPPH free radical scavenging abilities. Simulated digestion in vitro changed the antioxidant activities of the citrus peels.     

Advances in the in vitro digestion and fermentation of polysaccharides

In vitro digestion models are widely used to study the structural changes, digestion and release of food components under simulated gastrointestinal conditions. As compared to the in vivo digestion tests, the in vitro digestion reflects the digestion and utilisation of food after ingestion and has the advantages of being time consuming, inexpensive, reproducible and free from moral and ethical restrictions. This study reviewed the current research studies on the in vitro simulated digestion of polysaccharides conducted in the last 5 years and focused on the oral, gastric and intestinal digestion models, with the aim of providing a basis for the further testing of changes in the content, structure and active ingredients of polysaccharides before and after digestion.     

Microencapsulation of Bifidobacterium bifidum F‐35 in Whey Protein‐Based Microcapsules by Transglutaminase‐Induced Gelation

Abstract: Bifidobacterium bifidum F‐35 was microencapsulated into whey protein microcapsules (WPMs) by a transglutaminase (TGase)‐induced method after optimization of gelation conditions. The performance of these WPMs was compared with that produced by a spray drying method (WPMs‐A). WPMs produced by the TGase‐induced gelation method (WPMs‐B) had larger and denser structures in morphological examinations. Native gel and SDS‐PAGE analyses showed that most of the polymerization observed in WPMs‐B was due to stable covalent crosslinks catalyzed by TGase. The degradation properties of these WPMs were investigated in simulated gastric juice (SGJ) with or without pepsin. In the presence of pepsin, WPMs‐A degraded more quickly than did WPMs‐B. Finally, survival rates of the microencapsulated cells in both WPMs were significantly better than that of free cells and varied with the microencapsulation method. However, WPMs‐B produced by TGase‐induced gelation could provide better protection for microencapsulated cells in low pH conditions and during 1 mo of storage at 4 °C or at ambient temperature.     

Changes in in vitro protein digestion of retort‐pouched pork belly during 120‐day storage

To investigate the effect of long‐term storage on in vitro protein digestion of the retort‐pouched pork belly. The products were stored at 25 °C for 0, 30, 60 and 120 days and digested with pepsin and trypsin at each time point. SDS‐PAGE and LC‐MS‐MS were applied to separate and identify proteins and their digested products. In vitro protein digestibility decreased from 47.7% after 60‐day storage to 25.4% after 120‐day storage for the samples digested by pepsin, and from 63.9% to 45.7% for the samples digested by pepsin and trypsin at corresponding time points. LC‐MS‐MS demonstrated changes in peptide composition and abundance with storage time. Long‐term storage could deteriorate nutritive values of meat products by reducing digestible protein content.     

In vitro gastrointestinal digestion of liquid and semi-liquid dairy matrixes

Protein digestion in two liquid dairy matrixes with different heat treatments (pasteurized and sterilized milks) and in one semi-liquid dairy matrix (stirred-yogurt) was investigated using an in vitro gastrointestinal digestion model. After buccal digestion, significantly lower amount of soluble proteins were measured in yogurt than in both milks. This difference between dairy matrixes decreased during gastric digestion and disappeared at the end of the duodenal digestion upon the proteolytic action of pepsin and pancreatin. Electrophoresis pattern of digested mixtures showed that casein digestion began at the gastric phase and was slower for pasteurized milk than sterilized milk and yogurt. At the end of duodenal digestion, no more intact caseins were present in all the dairy matrixes while faint bands of whey proteins were still visible for pasteurized milk and yogurt. The release of free amino acids during the duodenal phase varied according to their nature (acid, basic, neutral or hydrophobic) and seems to be governed by the specificity of the enzymes. These results suggest that the severity of milk's heat treatment influences the kinetics of protein digestion, mainly during the gastric phase, and that the impact of processing has to be considered to study protein digestion in dairy products.     

Effect of in vitro‐simulated gastrointestinal digestion on the stability and antioxidant activity of blueberry polyphenols and their cellular antioxidant activity towards HepG2 cells

In this study we investigated the influence of in vitro‐simulated gastrointestinal digestion on the bioaccessibility and antioxidant activity of polyphenols from blueberries (Vaccinium spp.). Total phenolic, anthocyanin, and flavonoid content was determined, and extract and digesta compositions were analysed by HPLC‐ESI‐MS/MS. The phenolic compounds were relatively stable under a gastric environment, whereas polyphenols and anthocyanins were unstable under an intestinal environment. The bioaccessibility of polyphenol, anthocyanin, and flavonoid was greatly decreased after the intestinal digestion, and the recoveries were only 13.93%, 1.95%, and 15.68% (the IN sample), respectively. Polyphenolic profile alteration occurred during in vitro‐simulated gastrointestinal digestion. Changes of phenolic compound antioxidant activity during digestion correlated with polyphenol, flavonoid, and caffeic acid concentrations. Digested extract cellular antioxidant activity was lower than non‐digested extract activity (P < 0.05). Polyphenol dose–response correlations with cellular antioxidant activity were observed. These results indicated that in vitro‐simulated gastrointestinal digestion significantly impact polyphenols and their antioxidant activity.     

Effect of thermal processing and digestive protease on the antioxidant capacity of fruit juice–milk beverage model systems under simulated gastrointestinal digestion

The effects of thermal processing and digestive protease on the antioxidant capacity of fruit juice–milk beverage (FJMB) models containing whey protein (WP) and chlorogenic acid or catechin (CAT) under in vitro digestion were investigated. After gastric digestion, the FJMB showed a significant (P < 0.05) increase in ABTS, but little change in ferric reducing antioxidant power (FRAP). Intestinal digestion decreased the FRAP and increased ABTS except in the model containing 0.1% CAT. There were different effects (none, masking, synergistic effect) in the antioxidant activity of the WP and phenolics under digestion. Pasteurisation (63 °C/30 min) had no significant effect on the FJMB's antioxidant capacity, while sterilisation (121 °C/10 min) significantly (P < 0.05) increased, decreased or had no significant effect on ABTS and FRAP under digestion, depending on the model. Pepsin and pancreatin significantly (P < 0.05) decreased the fruit phenolics' ABTS. Ferric reducing antioxidant power was not significantly influenced by pepsin during gastric digestion, but was significantly (P < 0.05) decreased by pancreatin during intestinal digestion. These results would be helpful to improve the efficacy of fruit phenolics in FJMB subjected to thermal processing and to maintain the health benefits of this kind of functional products in the food industry.     

Bioactive Phaseolus lunatus peptides release from maltodextrin/gum arabic microcapsules obtained by spray drying after simulated gastrointestinal digestion

Bioactive peptides can be protected from the gastrointestinal environment by microencapsulation. The aim was to assess the effect of simulated gastrointestinal digestion on bioactive properties of P. lunatus peptides (ACE-I, α-glucosidase, α-amylase, and dipeptidyl peptidase-IV inhibition) microencapsulated by spray drying using maltodextrin/gun arabic in optimal formula. Microcapsules were formulated using a 2² factorial design. The simultaneous effect of P. lunatus hydrolysate (4 and 10 g 100 g⁻¹) and proportion of maltodextrin/gum arabic (25:75 and 75:25 g 100 g⁻¹) on yield, protein efficiency, size, protein release at pH 2.0 and pH 7.0 of the different microcapsules was studied. Microcapsules with maximum yield, protein efficiency, and protein release at pH 7.0, and minimum protein release at pH 2.0 were subjected to simulated gastrointestinal digestion. Microcapsules obtained in optimal formula preserved the α-glucosidase, α-amylase, and dipeptidyl peptidase-IV inhibitory activity of P. lunatus peptides after in vitro gastrointestinal digestion.     

Stability of antioxidant peptides from duck meat after post‐mortem ageing

The stability of antioxidant peptides from aged duck meat during processing and simulated gastrointestinal digestion was investigated. The antioxidant peptides preserved a high stability in the presence of diverse NaCl or upon various time heating. The antioxidant activities were strengthened by the addition of 4–8% glucose or by heating at 100 °C, whereas they were lost under alkaline conditions. During in vitro digestion, the antioxidant activities increased with pepsin treatment but then decreased following trypsin digestion. Pepsin hydrolysed peptides into short fragments and results in the increased exposure of internal hydrophobic amino acids. With further treatment by trypsin, peptides can be hydrolysed completely and more free amino acids were released, leading to the decline in surface hydrophobicity. These variations might be responsible for the change in antioxidant activity during in vitro digestion. The antioxidant peptides from aged duck with high stability can be used as functional food ingredients to improve human health.     

Fermented coconut jelly as a probiotic vehicle,physicochemical and microbiology characterisation during an in vitro digestion

There is little information on the survival of probiotics in plant-based foods after simulated gastric and intestinal conditions, likewise the microstructure arrangement in the no-dairy fermented food. This work aimed to study if the agar–agar in a fermented coconut jelly confers protection to probiotics, phenolic and antioxidant compounds during in vitro digestion. Samples containing higher agar–agar amounts tend to retain (P < 0.05) antioxidant and phenolic compounds in their network better, even after the in vitro digestion. Also, a compact and homogeneous microstructure was observed by the Confocal Laser Scanning Microscopy. The texture profile analysis shows that 1% of agar samples presented the maximum hardness (P < 0.05) due to more bonding points and intermolecular interactions. Finally, the survival of probiotics remained above the recommended values (10⁶–10⁷ CFU g⁻¹) after the in vitro digestion of a product with probiotic potential.     

Stability and antioxidant activity of anthocyanins from purple sweet potato (Ipomoea batatas L. cultivar Eshu No. 8) subjected to simulated in vitro gastrointestinal digestion

The study was aimed to investigate the stability and antioxidant activities of anthocyanins obtained from purple sweet potato via an in vitro digestion system. Three fractions of anthocyanin-rich extracts were obtained via ODS packing column. Anthocyanins and copigment (primary phenolic acids) of fraction 2 were investigated during simulated an in vitro gastrointestinal digestion. Anthocyanins and copigment were recognised by UPLC-LTQ-MS/MS. Besides, anthocyanins were found effectively stable under the acidic gastric digestion conditions. However, the anthocyanins recovery was greatly decreased at around 10% after intestinal digestion. An association between the type, number of acylated group and stability to intestinal digestion was found. Di-acylated anthocyanins possessed higher stability compared with mono-acylated anthocyanins and the stability of acylated group in digestion process followed the order of p-hydroxybenzoyl > feruloyl > caffeoyl. However, there was no much difference in copigment content which was found during digestion process. Moreover, the radical scavenging ability and xanthine oxidase (XO) inhibition showed that the digestion products possessed good biological activities mainly due to its anthocyanin composition.     

Solvent extraction and in vitro simulated gastrointestinal digestion of phenolic compounds from purple sweet potato

The total content of phenolic compounds in purple sweet potato (PSP) was determined and the release of such compounds from PSP in gastrointestinal digestion was studied in vitro. The extraction conditions for the maximum recovery of free phenol (FP) and bound phenol (BP) from PSP were determined by response surface methodology (RSM). The maximum recovery of FPPSP was 14.16 ± 0.87 mg GAE per g short for dry weight (DW), which was obtained using 60% (v/v) ethanol maceration with a liquid–solid ratio of 57.21:1 (mL g⁻¹) at 51.93 °C for 2.12 h. The maximum recovery for BPPSP was 7.54 mg GAE per g DW, which was obtained upon hydrolysis with 1.87 mol L⁻¹ NaOH at a liquid–solid ratio of 35.93:1 (mL g⁻¹) for 4.74 h. The maximum phenolic content was released after 1 and 2 h for the in vitro gastric and intestinal digestion respectively. The release of the phenolics was promoted by pepsin and gastric acid during gastric digestion, while it was further promoted by trypsin during intestinal digestion.     

Manipulating oral behaviour of food emulsions using different emulsifiers

This study aims to investigate the assumption that the presence of α-amylase in the human saliva will interact instantly with starch and will lead to very different oral behaviour and enhanced flavour release. Hence, orange oil flavoured emulsion was prepared with whey protein isolates (WPI) and modified starch (MS). The stability and flavour release of emulsions were examined through in vitro and in vivo studies. MS emulsion mixed with artificial saliva containing α-amylase resulted in more pronounced changes in mean particle size from 0.185 to 2.35 μm and a significant increase in viscosity. Morphology and turbidity revealed strong flocculation, coalescence and creaming. However, WPI emulsion exhibited very little changes in stability and behaviour. Similar results were observed during oral digestion (in vivo) for both emulsion systems. Moreover, a higher intensity of flavour release (37%) was observed in MS emulsion than WPI. This work demonstrated that a starch-stabilised emulsion has a very different oral behaviour to that of a protein-stabilised emulsion.     

Cooking does not impair the impact of pulsed electric field on the protein digestion of venison (Cervus elaphus) during in vitro gastrointestinal digestion

The present study was conducted to elucidate whether cooking impairs the positive effect of pulsed electric field (PEF) on the digestibility of venison during in vitro gastrointestinal protein digestion. Previous studies have used fresh uncooked meat to demonstrate the effect of PEF on protein digestibility during gastrointestinal digestion neglecting the effect that cooking could induce during meat preparation process. PEF-treated samples (T₁, 10 kV, 90 Hz, 20 µs) were cooked (core temperature of 75 °C) and subjected to in vitro simulated gastrointestinal protein digestion along with non-treated controls. A 3% increase of in vitro protein digestibility was found in cooked PEF-treated venison (P < 0.05). A positive (P < 0.05) impact of PEF processing was observed on overall protein digestion as measured by soluble protein (%) and SDS-PAGE. PEF did not change (P > 0.05) the release of minerals from cooked venison during digestion. Cooking had no negative influence on the mechanism through which PEF operates in improving the protein digestibility of venison.     

苦瓜皂苷与乳清蛋白水解物协同对二肽基肽酶-IV的抑制活性

为评价动植物源天然产物的二肽基肽酶-IV（dipeptidyl peptidase-IV,DPP-IV）抑制活性,以苦瓜皂苷（momordica saponins,MS）、乳清蛋白胃蛋白酶水解物（whey protein pepsin hydrolysates,WPPHs）、乳清蛋白胰蛋白酶水解物（whey protein trypsin hydrolysates,WPTHs）为原料,采用单因素试验和响应面分析优化水解条件,再将MS与WPPHs、WPTH进行复配,结合模拟体外消化,探究DPP-IV抑制活性。结果表明,MS、WPPHs及WPTHs具有DPP-IV抑制活性,最佳水解条件为：当酶添加量4%、pH 2.7酶解2 h时,WPPHs的DPP-IV抑制率最高为15.43%;当酶添加量4%、pH 7.6酶解4 h时,WPTHs的DPP-IV抑制率最高为14.62%。苦瓜皂苷与乳清蛋白水解物具有协同对二肽基肽酶-IV抑制活性作用,当MS与WPPHs、WPTHs的复配体积比均为1:1时,显著高于两者单独累加（p<0.05）。经胃消化后,WPPHs的DPP-IV抑制率降低2.02%,MS和WPTHs的DPP-IV抑制率升高0.99%、7.01%;经肠道消化后,WPPHs的DPP-IV抑制率升高2.23%,而MS和WPTHs的DPP-IV抑制率降低4.12%、2.70%。研究结果可为天然动植物源产物协同对二肽基肽酶-IV抑制活性提供了基础性数据,为降血糖功能性产品的开发提供新的方向。     

Characterisation of whey protein isolate–gum tragacanth electrostatic interactions in aqueous solutions

The main objectives of this study were to measure molecular parameters of gum tragacanth by GPC‐MALLS system and investigate the complexation behaviour of whey protein isolate/gum tragacanth mixed dispersions (0.5 wt% total biopolymer concentration) as a function of pH (7.00–2.00) and the biopolymer mixing ratio (r = 0.1–10) using spectrophotometric, zeta potential and precipitate yield determination methods. GPC‐MALLS revealed that gum tragacanth contains relatively heterogeneous particles with high weight‐average and number‐average (M_w = 7.74 × 10⁵ g mol^?1 and M_n = 3.87 × 10⁵ g mol^?1) molecular mass and high dispersity index (~2.04 ± 0.3). Results of complexation displayed that as the biopolymer mixing ratio increases, the net neutrality shifts to the higher pHs. The critical values associated with the complex structure formation were found at r = 2 in which the charge density of the mixture was near zero at a wide range of pH (3.0–4.0). However, the highest precipitate yield achieved in pH 3.4.