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

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

Foaming characteristics of oat protein and modification by partial hydrolysis

Foaming ability of oat protein isolate (OPI) was analysed at pH 4 and 7. Foaming properties were influenced by partial hydrolysis with trypsin (OPT) and alcalase (OPA). The viscoelasticity of the protein film, the interactions between the protein molecules, and the network forming within the protein film were analysed by interfacial rheology. At pH 7, foams made of OPI and OPT were found to be stable with OPI showing the fastest foaming ability. At pH 4, the foaming properties of OPI were found to be poor due to limited solubility. The specific cleavage pattern of trypsin resulted in peptides with improved foaming properties, especially at pH 4, resulting in a homogenous foam structure, a fast foaming ability, and a highly viscoelastic interfacial film. The formation of a thick steric protein layer at pH 7 and the formation of strong hydrophobic interactions at pH 4 were found to be the dominating foam stabilisation mechanisms. In conclusion, oat protein may serve as a food ingredient with targeted functional properties

Spray drying of emulsions: Influence of the emulsifier system on changes in oil droplet size during the drying step

The goal of this study was to investigate the influence of the emulsifier system on the changes in oil droplet size occurring during the drying step of spray drying of emulsions. Atomization and spray drying experiments were performed with emulsions stabilized with whey protein isolate (WPI) alone or in combination with low molecular weight emulsifiers (lecithin, mono- and diglycerides (MoDi), and citrem). Oil droplet coalescence was observed for the systems WPI/Citrem and WPI/MoDi, as the d$_{90,0}$ increased from 0.86 ± 0.16 and 1.67 ± 0.35 µm after atomization to 1.83 ± 0.24 and 1.90 ± 0.17 µm after drying, respectively. Oil droplets stabilized with WPI or WPI/Lecithin remained stable during drying. Measurements of dilatational rheology of the interfacial film showed that phase angle values increase in the order WPI/Lecithin < WPI < WPI/Citrem = WPI/MoDi. Therefore, in the studied system oil droplet coalescence during drying increases when the elastic behavior of the interfacial film decreases

Untersuchungen zur Strukturbildung von Milchprodukten

Eine gleichbleibend hohe Produktqualität determiniert maßgeblich die Akzeptanz beim Verbraucher und den Erhalt der Marktstellung. Dieses Ziel lässt sich nur realisieren, wenn eine Qualitätskontrolle der involvierten Prozesse und Rohmaterialien erfolgt. Vielfach existieren zur Qualitätsbeurteilung nur aufwendige analytische Methoden, die eine schnelle Kontrolle und ein unmittelbares Eingreifen verhindern. Mit dieser Arbeit sollen die Strukturbildung und -änderung im Verlauf verschiedener Prozesse in der Produktionstechnologie der Milchindustrie untersucht und Prüfprocedere entwickelt werden, die als Schnellmethoden ein kurzfristiges Bewerten der Rohstoffe und ein Eingreifen in den Produktionsprozess ermöglichen. Die labinduzierte Gerinnung wurde sowohl mit Rohmilch gesunder Kühe und Ziegen als auch mit Milch euterkranker Kühe durchgeführt. Ziel der Untersuchungen war eine Analyse der biochemischen Veränderungen des Caseins und der Strukturierungsmechanismen. Der Untersuchungsschwerpunkt umfasst die zeitliche Abfolge und Kopplung zwischen biochemischen Reaktionen am Casein und den Strukturveränderungen von der Milch zum Labgel durch inline-online-Erfassung der Prozessviskosität. Die Kinetik der enzymatischen Reaktion am Beispiel der Freisetzung von Caseinmakropeptid und die resultierenden Strukturbildungsmechanismen wurden untersucht und modelliert. Es zeigt sich ein deutlich abweichendes Verhalten der Milch von euterkranken Kühen. Durch Kopplung der Strukturparameter mit den Ergebnissen der hydrophoben Interaktionschromatographie werden Veränderungen am Caseinprofil der Milch von euterkranken Kühen nachgewiesen. Daher sollte diese im Rahmen der Promotion entwickelte Analytik in eine Eingangskontrolle der Milch aufgenommen werden. Bezüglich der Optimierung der Käseproduktion bietet die rheologische Methode eine Möglichkeit den optimalen Schneidezeitpunkt nicht mehr visuell zu beurteilen, sondern objektiv anhand der Endviskosität zu bestimmen. Die Untersuchungen zur Labgerinnung von Ziegenmilch dienen der Überprüfung der Übertragbarkeit der rheologischen und spektrophotometrischen Methode. Es werden klare Unterschiede zum Gerinnungsverhalten von Kuhmilch vor allem bei der Gelausbildung gefunden. Üblicherweise wird bei dem Prozess der Säuregerinnung (Joghurtproduktion) die Trockensubstanz der Prozessmilch erhöht, was unter anderem durch Zugabe von Molkenproteinkonzentratpulvern geschehen kann. Aus der Industrie ist das Auftreten einer erheblichen Anzahl von Fehlfermentationen bekannt, die in einer mangelhaften Funktionalität der Pulver begründet sind. Thermisch denaturierte Molkenproteinpulver bilden Partikelgele aus, was sich wiederum als Störgröße auf den Technologieablauf und die Produktqualität (Synärese) auswirkt. Es besteht daher ein großes wirtschaftliches Interesse an einer Schnellmethode zur Bewertung der Pulverqualität. In der vorliegenden Arbeit wird die Laserdiffraktometrie als Verfahren zur Bewertung des Lösungsverhaltens gewählt und die Anwendbarkeit durch eine umfassende Methodenentwicklung und verschiedene Untersuchungen bestätigt. Als wichtige dritte Produktionstechnologie in der Milchindustrie wird die Sprühtrocknung am Beispiel der Herstellung von Quarkpulver betrachtet. Hierbei muss besonders beachtet werden, dass es sich um ein plastisches, nicht NEWTONsches System handelt. Die Produktionstechnologie wird im Folgenden untersucht, wobei kritisch angemerkt werden muss, dass anstatt der üblichen Zerstäubung für hochkonsistente Produkte über eine Scheibe eine Düse gewählt wurde, die ursprünglich zur Trocknung von Magermilchkonzentrat ausgelegt war. Zudem wurde der Einfluss von Scherenergie und Wärme auf die Destrukturierung vor Trocknung untersucht.The production of dairy products of a consistently high quality significantly determines consumer acceptance and will occupy a similarly important market position in the future. This objective can be realized if a quality control of the involved processes and raw materials is undertaken. In many cases, only elaborate analytical methods exist which represent a barrier to a rapid control and direct intervention. In this work the structure formation and structural changes in the course of various processes in dairy production technology should be examined and methods should be developed, which facilitate a rapid grading of the raw materials and intervention in the production process. Rennet induced coagulation was investigated for raw bulk cow and goat milk as well as for milk from infected udder quarters of cows. Experiments were carried out to gain more scientifically based information on biochemical changes of the casein and the mechanism of structuring during rennet induced coagulation. The main focus of the research was the time dependent coupling between the biochemical reaction of the casein and the structural change from the fluid milk to the rennet gel by inline-online detection of the process viscosity. The kinetics of the enzymatic reaction─the release of caseinmacropeptide─and the resulting structuring mechanisms were examined and modeled. A significantly different behavior of milk from infected udder quarters was detected. The structure parameter in combination with the hydrophobic interaction chromatography results proved an altered casein profile. It is imperative that the analytical method which was developed as part of this thesis be included in milk grading. Concerning an optimized cheese production, the rheological method offers the possibility to determine the optimal cutting time not only from a subjective but also from an objective position by calculated projection of the end viscosity after a definite time period. The investigations dealing with the rennet induced coagulation of goat milk were done to verify the transferability of the rheological and spectrophotometric method. Significant differences were detected between the rennet induced coagulation of cow and goat milk especially between the gel formation. Commonly, during the process of acid induced coagulation (yoghurt production) dairy powders are used to increase the dry matter of the process milk which is often done by addition of whey protein concentrate powder. It was found that in the production flow a large share of defective fermentations might occur, which are related to defective functionality of the powders. Thermal denaturation of whey proteins leads to the development of particle gels which act as a disturbance variable during the production process and for the product quality (syneresis). As a result, the development of a rapid method for the assessment of the powder quality is of great economic interest. The principle of laser diffraction was chosen in the present work for the assessment of the rehydration behavior and the applicability of this method has been confirmed by an extensive method development and diverse experiments. The third important production technology in the dairy industry─spray drying─is viewed exemplarily for the production of quark powder. Attention should be paid to the fact that quark is a plastic, non NEWTONIAN system. In the following, production technology systems are investigated. It has to be remarked here that atomization was done via nozzle instead of the commonly used wheel atomization for highly consistent products. The nozzle geometry typically was designed for the drying of skim milk concentrate. Additionally, the influence of shear energy and temperature on the structure deformation before drying was investigated

Interfacial properties of β-Lactoglobulin at the oil/water interface: influence of starch conversion products with varying dextrose equivalents

In spray dried emulsions, frequently milk proteins are used as interfacial active components and starch conversion products are added as matrix material at high concentrations. To characterize interfacial properties at the oil/water interface by commonly applied methods, low protein, and carbohydrate concentrations from 1 to 2% are usually analyzed. The impact of a higher concentration of starch conversion products was not investigated so far. Therefore, the formation and rheological properties of β-lactoglobulin (β-LG) stabilized films at the oil/water interface were investigated via short and long-time adsorption behavior using pendant drop tensiometry as well as dilatational and interfacial shear rheology. Suitability of the applied methods to the chosen samples with higher concentrations >1–2% was verified by calculation of selected key numbers like capillary number and by detailed reviewing of the results which is summarized further on as key indicators. It is hypothesized, that the increase in concentration via presence of starch conversion products will delay interfacial stabilization as a result of increased bulk viscosity with decreasing degree of degradation (dextrose equivalent) of the starch. Furthermore, this increase in concentration leads to more stable interfacial films due to thermodynamic incompatibility effects between protein and starch conversion products which results in increases of local protein concentration. Key indicators proved a general suitability of applied methods for the evaluation of the investigated samples. Moreover, results showed an increase in interfacial film stability and elastic properties alongside a decreased interfacial tension if starch conversion products were present in a high concentration.TU Berlin, Open-Access-Mittel – 202

Functional properties of chickpea protein-pectin interfacial complex in buriti oil emulsions and spray dried microcapsules

The aim of the present study was to investigate the impact of chickpea protein (CP) alone or in the form of sequentially adsorbed chickpea protein and high methoxylated pectin (CP-HMP) on the microencapsulation of buriti oil by spray drying. CP was extracted and characterized by its molecular weight distribution, zeta potential and solubility. The adsorption of CP and CP-HMP complexes to the oil/water (O/W) interface was investigated by measurement of the interfacial tension. The intractions between the molecules at the O/W interface were analyzed by interfacial shear rheology. Emulsions containing CP or CP-HMP were prepared at pH 3.5, homogenized and spray dried at 180/70 ºC and 210/90 ºC (inlet/outlet) temperature. The oil droplet size distribution (ODS) of emulsions before and after spray drying, the encapsulation efficiency (EE) of microcapsules and their oxidative stability were evaluated. The interfacial tension of CP at the O/W interface was not affected by pectin addition. However, interfacial shear rheology revealed strong interactions between CP-HMP complexes, maintaining the physical integrity of emulsion oil droplets during spray drying. On the other hand, interactions in the CP film were weaker and the droplets were affected by spray drying, suffering from an increase in size. The EE of CP-HMP microcapsules was higher than for CP microcapsules, which suggests a synergistic effect. The spray drying temperature had no effect on the EE. During six months of storage, a slight increase of the conjugated dienes content was observed for all microcapsules. However, the type of microcapsule and the temperature of spray drying had no effect on the development of lipid oxidation

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

BACKGROUND: During the industrial production of β-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 subjecting to heat treatment to assure starch gelatinization. RESULTS: In detail, the process of yoghurt production involved an initial heating step to 90 °C, subsequently 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-value 4.2) with a certain amount of lactic acid (3.3±0.2 g kg-1) and contained 4.9∙106 cfu g-1 of lactobacillus after 24 h of fermentation. SEM revealed a porous network presumably built up from the gelatinized starch fraction containing aggregated structures in-between which were assumed to be aggregated oat proteins. Moreover, to a limited extent, proteolysis occurred during fermentation. Thus, some of the proteolytic enzymes being 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

Towards an improved understanding of spray-dried emulsions: Impact of the emulsifying constituent combination on characteristics and storage stability

In spray-dried emulsions a wide range of emulsifying constituents including proteins and low molecular weight emulsifiers are used. Due to their different behaviour, combinations of different emulsifying constituents are common, whereupon their interactions may also adversely affect powder properties and stability. Therefore, the impact of whey protein isolate alone or in combination with lecithin, mono-/diglyceride and citrem as low molecular weight emulsifiers on powder characteristics and storage stability were investigated. Temperature stresses were applied to induce instability phenomena. A specific combination of protein and low molecular weight emulsifiers resulted in a reduction in oil droplet size while maintaining encapsulation efficiency. Induction of crystallisation through low temperature stress induced oil release in samples, in which templating for heterogeneous nucleation took place. High temperature stress caused Maillard reaction, protein-fat complexation and phase transition of the matrix resulting in colour changes and reduction of extractable oil