Functionalisation of pea protein by tryptic hydrolysis – Characterisation of interfacial and functional properties

With regard to applications in dispersed systems (i.e. emulsions), improving the poor solubility of pea protein in the pH-range applicable to foods (pH 3 to pH 7) is a prerequisite. To achieve this, a pea protein concentrate was produced on a lab scale using alkaline extraction and subsequent enzymatic hydrolysis to degrees of 2 and 4%. Solubility was improved and interfacial properties were influenced. All samples led to the formation of emulsions but displayed a tendency towards wider oil-droplet size distributions at pH close to the isoelectric point. Using microscopy, this increase could be attributed to the formation of aggregates, which in turn can be ascribed to lack of repulsion caused by the low absolute values of ζ-potentials. The same lack of repulsion led to stronger and more elastic interfacial films at pH 4 and 5 than at pH 7. Moreover, film strength increased significantly with increasing degree of hydrolysis. Dilatational experiments imply that hydrolysis enhances in-plane structural rearrangements. Thus, it is concluded that tryptic hydrolysis has the potential to improve the overall stability of emulsions.BMBF, 01EA1408C, Kompetenzcluster Ernährungsforschung: NutriAct - Ernährungsintervention für gesundes Altern, Technische Universität Berli

Thermally induced degradation of citrus pectins during storage – Alterations in molecular structure, colour and thermal analysis

Commercial citrus pectins (17 samples from 3 different suppliers) were stored at 60 °C and 80% humidity for two weeks. Molecular parameters (galacturonan content, degree of methoxylation, intrinsic viscosity), colour and behaviour in thermal analysis (DSC and TG) were tested and the results were compared with those of model pectins prepared under laboratory conditions from a previous study. Whereas the molecular parameters and colour of both groups changed similarly, considerable differences in the thermal analysis were found not only between model pectins and commercial pectins but also between commercial samples from different suppliers. It seems that varying processing conditions between laboratory preparations and industrial processing as well as differences in industrial scale processing influence the pectin properties and their degradation during storage. All commercial citrus pectin samples were strongly demethoxylated and depolymerised, former high-methoxylated pectins with degree of methoxylation (DM) > 50% became low-methoxylated with DM < 50% and some low-methoxylated samples afterwards had a DM close to pectic acid. As a result, also their gelation properties changed markedly. For pectin producing and applying companies it might be essential to check the properties of pectins after longer storage under unfavourable conditions. As a consequence, a variation of the gelation conditions for pectins after storage might be necessary

Structure formation in sugar containing pectin gels - Influence of gel composition and cooling rate on the gelation of non-amidated and amidated low-methoxylated pectin

Gel structure formation and gel properties of low-methoxyl pectin (LMP) and low-methoxyl amidated pectin (LMAP) with similar degree of methoxylation have been investigated by oscillatory rheological measurements. The gelling process was examined in a sugar-acid environment matching the conditions in jams and jellies. Factors studied included cooling rate, calcium content and pH. Parameters derived from the rheological measurements comprised the gel point, structuring velocity, initial and critical structuring temperature, average structuring developing rate and loss factor (tanδend). The influence of the cooling rate on the gelling process of LMP was moderate and the influence on the final gel properties was significant, tanδend decreased with increasing cooling rate. The calcium content significantly affected the structuring process of LMAP and the final gel properties. At high calcium content, the gelling process started at a higher temperature but the resulting gels were less strong. The pH had a significant but partly opposite effect on the gelation of LMP as well as LMAP. The differences in gelation behavior between LMP and LMAP can be explained by the lower number of available blocks of free carboxyl groups in LMAP as well as by the formation of additional hydrogen bonds through the amide groups

Influence of enzymatic and acidic demethoxylation on structure formation in sugar containing citrus pectin gels

Aim of the present study was to investigate the impact of different demethoxylation methods and the co-occuring side effects on the molecular properties and structure formation in pectin gels. A high-methoxylated citrus pectin (HMP) was demethoxylated using either hydrochloric acid or pectin methylesterases of plant (pPME) or fungal (fPME) origin. pPME treatment causes a more block-wise distribution of free carboxyl groups, fPME or acidic treatment a random distribution. Twelve pectin samples with four different degrees of methoxylation (DM) between 62% and 41% were prepared. The gelation process was studied by oscillatory measurements. In pectin samples from pPME treatment structure formation started at higher temperature and the final gels were more elastic in comparison to pectin from the two other modifications. The impact of the block-wise distribution of the free carboxyl groups became more evident with decreasing DM. The gelling process of pectin samples with random distribution was similar independent of DM.Side effects of all demethoxylation reactions were an altered sodium ion content (high in enzymatically treated pectin, close to zero in acidic treated) and a decrease of the molecular weight with increasing degree of demethoxylation. These side effects additionally altered the gelation process and the final gel properties in different ways

Structure formation and rheological properties of pea protein-based gels

Nutritional recommendations for the elderly, but also the general public, include incorporation of plant proteins in the diet, an increase in the intake of Ω-3 fatty acids and an increase in intake of dietary fibre. Protein structure and structuring behaviour of plant proteins differ from that of milk proteins. Therefore, the aim of the presented study was to characterise the structuring process and resulting structure of yoghurt-style gels containing 10% pea protein with and without addition of nutritionally recommended ingredients like rapeseed-oil and/or commercial oat fibre. Rheological measurements were combined with microscopy for sample characterisation. Generally, all studied formulations were able to form acid induced gels via fermentation. The acidification led to a two-phase gelation process resulting in thick gels that showed mainly weak rheological behaviour. Supplementation with oil and/or fibre resulted in an increase of the relative concentration of pea protein in the aqueous phase and led to a strong increase in the complex shear modulus |G*| as well as the maximum structuring velocity d|G*|/dt. These effects need to be considered when tailoring yoghurt-style gels with high consumer acceptance.BMBF, 01EA1408C, Kompetenzcluster Ernährungsforschung: NutriAct - Ernährungsintervention für gesundes Altern, Technische Universität Berli

Towards By-Product Utilisation of Pea Hulls: Isolation and Quantification of Galacturonic Acid

In order to evaluate by-products from food processing as alternative raw materials for pectin extraction, their amount of galacturonic acid (GalA) has to be analysed as a marker for pectin content. In the present study, significant differences in GalA release using different digestion methods are shown for pea hulls, as an example of by-products with a high content of cellulose. Complete digestion of the fibre matrix was assumed for Saeman hydrolysis as a reference protocol. Significantly lower GalA release was achieved by a treatment with trifluoracetic acid (TFA). An alternative treatment with ethylenediaminetetraacetic acid (EDTA) at pH 11 followed by an enzymatic digestion at pH 4.5 using a combination of polygalacturonase (Vegazyme M) and cellulase (Celluclast 1.5L) resulted in a similar release of GalA compared to Seaman hydolysis. Pea hull samples, analysed by this alternative protocol, showed on average a GalA content of 11.2%. Therefore, pea hulls may serve as new raw material for pectin extraction.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Modification and physico-chemical properties of citrus pectin – Influence of enzymatic and acidic demethoxylation

Aim of the present study was to investigate the effect of the method of demethoxylation on the particle structure and techno-functional properties of pectins with different degree of methoxylation and distribution of free carboxyl groups. Two groups of model pectins, one with 57% and one with 42% degree of methoxylation have been prepared from one single commercial pectin. Modifications were performed by an acidic and two enzymatic methods using fungal and plant-derived pectin methyl esterases. Thermal stability was investigated by thermal analysis and water uptake was determined by a sorption and a capillary sucking method. The enzyme-treated pectins were thermally less stable than the acid-treated. The water uptake of enzyme-treated pectins was higher than in acid-treated samples in the sorption method and lower in the capillary sucking tests. The different behaviour is explained by differences in pH during demethoxylation and a co-occurring variation in sodium content. Both parameters affected intermolecular interactions of the pectin macromolecules in solution, which resulted in differences in the particle morphology. The effect of the distribution of free carboxyl groups (statistical or block-wise) on the techno-functional properties was more pronounced in high-methoxylated pectins than in low-methoxylated pectins

Thermal degradation of citrus pectin in low-moisture environment - Influence of acidic and alkaline pre-treatment

Pectin powder is degraded during storage and transport by demethoxylation and depolymerisation. The degradation mechanisms and especially the influence of pre-treatments on the degradation reactions are not completely understood. In this study, commercial citrus pectin was modified by either acidic or alkaline demethoxylation. The modified pectins, as well as the commercial pectin, were thermally degraded during four weeks of storage at 60 °C and 80% relative humidity. Demethoxylation and depolymerisation as well as colour alterations were examined during degradation, and the course of the reactions was monitored. It was found that the type of pre-treatment during modification determined the material properties and, thus, the water uptake of the modified pectin powders. The resulting water availability in the samples was crucial to the extent of demethoxylation and to the type and intensity of depolymerisation since some of these reactions competed for the water in the climate chamber. The pre-treatment also determined the content of neutral sugars and sodium ions of the modified pectins. High contents of these components limited the extent of degradation in different ways. A previously assumed third depolymerisation mechanism of pectins, beside backbone hydrolysis and β-elimination, was confirmed.DFG, 268547215, Strukturabhängige Abbaureaktionen von Pektinen und deren Auswirkungen auf nicht-enzymatische Bräunung und technologische Funktionalitä

Enrichment of yoghurt with oat protein fractions: Structure formation, textural properties and sensory evaluation

Despite its excellent nutritional properties, unlike other cereals oat displays poor baking properties and therefore is mainly processed in products like rolled oats or serves as raw material for the functional ingredient β-glucan. During β-glucan production, a protein-rich fraction remains as a by-product. Functionalisation of this protein-rich oat-fraction and its application as a valuable food ingredient would improve the sustainability of the process. In the present study, oat protein-enriched cow's milk yoghurt was produced. The main foci were on the characterisation of techno-functional properties, as well as on the analysis of the organoleptic perception and sensory properties by a trained panel. Cow's milk yoghurt, following a traditional formulation with addition of skim milk powder (SMP), served as a reference. Oat protein was incorporated using two preparations: oat protein concentrate (OPC) and oat protein isolate (OPI). Fermentation of yoghurt enriched with SMP, OPC or OPI was monitored via pH-value, formation of lactic acid and rheological measurements. In addition, texture analysis and measurement of syneresis were performed and sensory properties were evaluated. Yoghurt containing SMP showed the highest strength in texture analysis but also a high rate of syneresis. Addition of OPC resulted in a product, which combines nutritional benefits with the sustainable use of the by-product of oat processing as well as improved product quality with respect to syneresis and sensory evaluation, especially mouthfeel. In case of OPI, strong sedimentation took place and high syneresis was observed. It is assumed that the compatibility of oat protein with milk proteins is low, which may be compensated by gelatinisation of starch during yoghurt production

Towards an increased plant protein intake: Rheological properties, sensory perception and consumer acceptability of lactic acid fermented, oat-based gels

In general, the interest in food that contains a reasonable amount of plant protein is steadily increasing. As a consequence, products with pleasant texture and taste ensuring a high consumer acceptance are needed. The aim of the present study was to develop and characterize structural differences and organoleptic impressions of lactic acid fermented, oat-based gels which could serve as plant protein enriched, non-dairy yoghurt alternatives. Oat protein concentrate, a by-product of cereal processing, was used as plant protein source. It was shown that total solids content had the highest impact on rheological properties. All samples were described as soft fluid gels and their structure was dominated by the heat-induced gelation of starch. Within this mixed food system of starch and protein, swollen starch granules, protein aggregates and residual small fat droplets were embedded in a rough macromolecular network of leached amylose. They acted as filler and increased the rigidity (G′) of the system. Native starch content determined the water holding capacity with an increase in water binding with increasing concentration. Overall, rheological characteristics were found to be strongly linked to the products’ textural attributes which, in turn, determined consumer acceptability. For the purpose of product development, overall liking was influenced by the quantifiable sensory attributes – sweet, moist, soft, and smooth. Purchase intention, however, was positively influenced by the extrinsic attribute information (on oat protein enrichment). These data, in combination with the impact of the identified ingredients on product structure, are a valuable tool to improve product properties, consumer perceptions and product acceptability. To conclude, lactic fermented, oat-based gels can serve as a plant-based yoghurt-alternative that combines nutritional benefits with good textural properties