Double emulsions for iron encapsulation: is a high concentration of lipophilic emulsifier ideal for physical and chemical stability?

BACKGROUND: Worldwide iron deficiency in diets has led to a growing interest in the development of food-compatible encapsulation systems for soluble iron, which are able to prevent iron's undesirable off-taste and pro-oxidant activity. Here, we explore the use of double emulsions for this purpose, and in particular, how the lipophilic emulsifier (polyglycerol polyricinoleate, PGPR) concentration influences the physicochemical stability of water-in-oil-in-water (W1 /O/W2 ) double emulsions containing ferrous sulphate in the inner water droplets. Double emulsions were prepared with sunflower oil containing 10 to 70 g kg-1 PGPR in the oil phase, and were monitored for droplet size distribution, morphology, encapsulation efficiency (EE) and oxidative stability over time. RESULTS: Fresh double emulsions showed an initial EE higher than 88%, but EE decreased upon storage, which occurred particularly fast and to a high extent in the emulsions prepared with low PGPR concentrations. All double emulsions underwent lipid oxidation, in particular those with the highest PGPR concentration, which could be due to the small inner droplet size and thus promoted contact between oil and the internal water phase. CONCLUSION: These results show that a too high PGPR concentration is not needed, and sometimes even adverse, when developing double emulsions as iron encapsulation systems. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The proteomic evidence on protein oxidation in pea protein concentrate-based low-moisture extrudates and its inhibition by antioxidants derived from plant extracts.

This study aimed to assess the antioxidant activity of golden chlorella (GoC) and grape pomace (GrP) extracts both in vitro and in pea protein-based extrudates. We hypothesized that GoC/GrP would limit oxidation of proteins in the extrudates compared with commercial antioxidants. The results showed that GoC extract was effective in metal chelation and GrP extract possessed excellent radical scavenging activity and reducing power. Protein oxidation inevitably occurred after low-moisture extrusion in terms of elevated level of protein carbonyls and the gradual loss of thiols. LC-MS/MS revealed that the monoxidation and 4-hydroxynonenal adduction were the major oxidative modifications, and legumin was the most susceptible globulin for oxidation. The GoC/GrP extracts effectively retarded the oxidation progress in extrudates by lower intensity of oxidized peptides, whereas protein electrophoretic profiles remained unaffected. This study highlighted the great potential of GoC/GrP as natural antioxidants in plant-based foods.

Protein blends and extrusion processing to improve the nutritional quality of plant proteins.

Plant proteins have low protein nutritional quality due to their unbalanced indispensable amino acid (IAA) profile and the presence of antinutritional factors (ANFs) that limit protein digestibility. The blending of pulses with cereals/pseudocereals can ensure a complete protein source of IAA. In addition, extrusion may be an effective way to reduce ANFs and improve protein digestibility. Thereby, we aimed to improve the protein nutritional quality of plant protein ingredients by blending different protein sources and applying extrusion processing. Protein blends were prepared with pea, faba bean, quinoa, hemp, and/or oat concentrates or flours, and extrudates were prepared either rich in pulses (texturized vegetable proteins, TVPs) or rich in cereals (referred to here as Snacks). After extrusion, all samples showed a reduction in trypsin inhibitor activity (TIA) greater than 71%. Extrusion caused an increase in the total in vitro protein digestibility (IVPD) of TVPs, whereas no significant effect was shown for the snacks. According to the molecular weight distribution, TVPs presented protein aggregation. The results suggest that the positive effect of decreased TIA on IVPD is partially counteracted by the formation of aggregates during extrusion which restricts enzyme accessibility. After extrusion, all snacks retained a balanced amino acid score whereas a small loss of methionine + cysteine was observed in the TVPs, resulting in a small reduction in IAA content. Thus, extrusion has the potential to improve the nutritional quality of TVPs by reducing TIA and increasing protein digestibility.

Associating Compositional, Nutritional and Techno-Functional Characteristics of Faba Bean (Vicia faba L.) Protein Isolates and Their Production Side-Streams with Potential Food Applications.

Faba beans (Vicia faba L.) show exciting prospects as a sustainable source of protein and fibre, with the potential to transition to a more sustainable food production. This study reveals the compositional, nutritional and techno-functional characteristics of two protein isolates from faba beans (Vicia faba L.), a high-starch fraction and a high-fibre side-stream. During the analysis of those four ingredients, particular attention was paid to the isolates' protein profile and the side-streams' carbohydrate composition. The isoelectric precipitated protein isolate 1 showed a protein content of 72.64 ± 0.31% DM. It exhibited low solubility but superior digestibility and high foam stability. High foaming capacity and low protein digestibility were observed for protein isolate 2, with a protein content of 71.37 ± 0.93% DM. This fraction was highly soluble and consisted primarily of low molecular weight proteins. The high-starch fraction contained 83.87 ± 3.07% DM starch, of which about 66% was resistant starch. Over 65% of the high-fibre fraction was insoluble dietary fibre. The findings of this study provide a detailed understanding of different production fractions of faba beans, which is of great value for future product development.

Oxidative stability of soy proteins: From ground soybeans to structured products.

The production of soy protein-based foods requires multiple-step, intensive processing and storage of soy ingredients, which can increase the product's susceptibility to oxidation. Therefore, we investigated the oxidative stability of soy protein-based products subjected to different relevant conditions or treatments: over storage of soy flours, over fractionation to yield soy protein isolate (SPI), and over subsequent thermomechanical processing to yield a model structured product. Soy flours were stable to lipid and protein oxidation over 250 days storage in chilled or ambient conditions. The fractionation process applied to make SPI did not increase substantially protein carbonylation, but increased surface-exposed hydrophobicity and decreased free thiols, compared to the starting defatted flour. Subsequent processing of hydrated SPI powder at 140 °C further increased protein carbonylation to a high extent. Therefore, we conclude that soy flours can be stable over long storage times, but processing to yield structured foods products promote protein oxidation.

Protein Oxidation and In Vitro Gastric Digestion of Processed Soy-Based Matrices.

Process conditions that are applied to make structured soy-protein-based food commonly include high temperatures. Those conditions can induce protein oxidation, leading to a decrease in their susceptibility to proteolysis by digestive enzymes. We aimed to investigate the effects of thermomechanical processing on oxidation and in vitro gastric digestion of commercial soy protein ingredients. Samples were sheared at 100 to 140 °C and characterized for acid uptake, carbonyl content, electrophoresis, and surface hydrophobicity. The enzymatic hydrolysis was determined in simulated gastric conditions. Protein ingredients were already oxidized and showed higher surface hydrophobicity and hydrolysis rate compared with those of the processed matrices. However, no clear correlation between the level of carbonyls and the hydrolysis rate was found. Therefore, we conclude that gastric digestion is mostly driven by the matrix structure and composition and the available contact area between the substrate and proteolytic enzymes.

Tayloring W/O/W emulsion composition for effective encapsulation: The role of PGPR in water transfer-induced swelling.

The role of the lipophilic surfactant, polyglycerol polyricinoleate (PGPR) in water transfer in food-grade double emulsions was investigated, and related to physical emulsion stability. Double (W/O/W) emulsions were prepared with various PGPR concentrations (0.5-5.0 wt%) in the oil phase, at initial osmotic pressure differences of up to 1.1 MPa between the water phases. At high PGPR concentrations (>2 wt%), emulsions showed good physical stability, with encapsulation efficiency close to 100%. It was found that PGPR is involved in water transfer between the water phases through reverse micelle formation by PGPR molecules or hydrated monomers of PGPR, and this allows for controlled swelling. Emulsions that are initially of low viscosity (milk-like emulsions), obtain an apparent viscosity of up to 3 Pa·s, and this effect can be used to tune the emulsion properties to the targeted application, whithout the need to gel either the internal or external phase.