Heat denaturation of soy glycinin : structural characteristics in relation to aggregation and gel formation

key words: soy protein; glycinin; thermal stability; pH; ionic strength;genetic variant; solubility; gelationThe main aim of this thesis was to study structural changes of soy glycinin at different conditions (pH and ionic strength) during thermal denaturation and their effect on aggregation and gel formation. The results show that, generally, glycinin is predominantly present in the 7S form at pH 3.8, while at pH 7.6 the major component is the 11S form. When, at ambient temperatures, the ionic strength at pH 7.6 is lowered from 0.5 to 0.2 or 0.03 the basic polypeptides within the glycinin molecule shift more to the exterior of the glycinin complex. This structural reorganisation caused the pH of minimal solubility to shift to higher values. The 7S form, which is more unfolded than the 11S form, denatures at a lower temperature than the 11S form. Changes in secondary structure take place simultaneously with denaturation. While at I = 0.03 the gels were found to be fine stranded, gel coarseness increased when the ionic strength was higher. At I = 0.03 finer gel network structures were formed at pH 3.8 than at 7.6, whereas for I = 0.2 and 0.5 the reverse was found. The observed differences in gel stiffness did not correspond to coarseness. The gel structure was clarified into more detail by the use of physico-chemical and spectroscopic techniques. The nature of the primary network particles was different at pH 7.6 (basic polypeptides) than at pH 3.8 (acidic and basic polypeptides). The heat denaturation process develops at 1% protein similarly as the heat denaturation process at 10% protein. However, the final gel structure and strength cannot be predicted from measurements performed at 1% protein. The heat denaturation mechanisms were not solved into more detail due to the fact that the genetic variants of glycinin differ in thermostability. It was found that the denaturation temperatures of these variants increase in the order G1/G2/G3/&lt; A4&lt;G5&lt;G4.</p

Insects as a sustainable feed ingredient in pig and poultry diets : a feasibility study = Insecten als duurzame diervoedergrondstof in varkens- en pluimveevoeders : een haalbaarheidsstudie

A feasibility study to explore application of insects as a sustainable high protein feed ingredient for pig and poultry diets was conducted on request of the Dutch Ministry of Economic Affairs, Agriculture and Innovation. This feasibility study comprised a desk study and a workshop with participants representing the various links in the “insect chain”. The objective of the study was to list, in a joint initiative of industrial stakeholders and scientists, how insects can be used on a large scale as an alternative protein source in feed for pigs and poultry

Rheological properties of acid skim milk gels as affected by the spatial distribution of the structural elements and the interaction forces between them.

The modulus, fracture stress and fracture strain of acid-induced skim milk gels prepared from preheated skim milk that was aged for 1200 min depended strongly on pHheating. The role of gel structure regarding the effect of pHheating on gel modulus and fracture stress and strain is discussed. Milk preheated at pH 6.20 gave finer stranded gels likely containing more curved strands with probably less S-S interactions than gels from pHheating 6.90 milk. The lower stiffness of gels made from pHheating 6.20 milk could be explained by a combined effect of differences in strand curvature, gel coarseness and S-S interactions, and the lower fracture stress by a combined effect of gel coarseness and S-S interactions whereby the first effect is opposite to and overruled by that of the S-S interactions. The lower modulus and fracture stress of gels from unheated milk could be explained by a combination of strand curvature and less S-S interactions, and by less S-S interactions alone, respectively

Acid skim milk gels: The gelation process as affected by preheated pH

The effect of preheating milk (10 min 80 [degree sign]C) at pH values from 6.20 to 6.90 on formation of acid skim milk gels was studied by dynamic oscillation measurements. Up to pH 6.65 a higher pH of heating (pHheating) resulted in a higher G'. Since below pH 4.9 the development of G'(pH)/G'(pH=4.9) and tan [delta] (pH) was similar we assume that the rearrangement processes happening below pH 4.9 were similar for all pHheating values studied. Based on data for tan [delta], G'(pH) and the pH of gel formation, it was hypothesized that the differences in moduli with pHheating stem from differences in the aggregation and rearrangement processes occurring before and just after gelation (pH>4.9). These differences are partly due to greater involvement of S-S interactions at higher pHheating. Furthermore, the soluble whey protein aggregates formed during preheating are in part not incorporated in the network, the extent depending on pH

Edible insects: The value chain

How can we face the challenge of future nutrition security? Insects offer a high quality, efficient and sustainable alternative to the common protein sources, and have the capacity to valorise organic side streams. As such, insects can close the loop in a circular economy. The current issue of Journal of Insects as Food and Feed is related to the international conference 'Edible insects: the value chain'. The papers presented link to research related to rearing, processing, nutrition and health, and consumer behaviour. Future chain development would benefit from further multi- and interdisciplinary knowledge gain. Also, other factors are important, like business development, enabling regulation, increased marketing and promotion, and fostering industrial partnership. These activities require collaboration among the actors within the insect chain.</p

Extracting Tenebrio molitor protein while preventing browning: effect of pH and NaCl on protein yield

The potential of insects as an alternative protein source for food applications was investigated by studying the effect of pH and NaCl on extraction yield of water-soluble proteins from Tenebrio molitor, while preventing browning due to polyphenol oxidation. Minimum protein solubility (29.6%) was at pH=4-6 and maximum (68.6%) at pH=11. Protein extraction at 0.1 M NaCl, pH=10 gave a recovery of 100%. The observed increase in browning at pH=8-11 corresponded to a lower monomeric phenol content. Sodium bisulphite (studied from 0.5-4%) could prevent browning, whereas ascorbic acid (studied in the range 0.01-0.04%) could not prevent as strong as sodium bisulphite. After acid precipitation (pH=4) an isolate with a protein content of 74% (yield of 22% of total protein) was obtained. It was observed that proteins from T. molitor behave more or less the same as proteins from meat and fish with respect to aqueous extraction, which is of relevance for food industry when using T. molitor protein as an ingredient in food products