A study of starch gelatinisation behaviour in hydrothermally-processed plant food tissues and implications for in vitro digestibility

The aim of this study was to investigate the role of the plant food matrix in influencing the extent of starch gelatinisation during hydrothermal processing, and its implications for starch digestibility. Differential scanning calorimetry (DSC) was used to provide a detailed examination of the gelatinisation behaviour of five distinct size fractions (diameters <0.21 to 2.58 mm) of milled chickpea and durum wheat. Gelatinisation parameters were obtained from the DSC thermograms and concomitant microscopy analyses were performed. The estimated terminal extent of gelatinisation (TEG) was compared with our previously published data for in vitro starch digestibility of the same food materials. We observed clear differences in the gelatinisation behaviour of matched size-fractions of chickpeas and durum wheat. In chickpea materials, the TEG values (34–100%) were inversely related to particle size, whereas in durum wheat, no sizedependent limitations on TEG were observed. The TEG values were completely consistent with the extent of starch amylolysis in all size fractions of both durum wheat and chickpea. Microstructural analysis following hydrothermal processing confirmed the presence of some partially gelatinised birefringent starch within intact chickpea cells. Birefringent starch granules were not present in any of the processed fractions of durum wheat. The differences in gelatinisation behaviour of these plant species seem to reflect the individual cell wall properties of these materials. These findings demonstrate the applicability of DSC to real food materials to provide insight into the mechanisms by which the food matrix (particularly the plant cell walls) influences gelatinisation, and consequently, starch amylolysis

Modelling the cooking process of a single cereal grain

Four models are developed to assist with the uniform and accurate cooking of whole grains for Uncle Tobys breakfast cereals. 1. Heat satisfies a linear conduction equation and is found to rapidly penetrate the grain. 2. Moisture satisfies a non-linear diffusion equation, and is found to penetrate the grain more slowly than heat. The more sophisticated moisture diffusion model is solved by numerical and analytic techniques for spherical and ellipsoidal grains. A vital role is played in the moisture diffusion model by the concept of the mean action time for wetting a grain. These first two models are used to determine sensitivity to key cooking parameters, and to calculate the degree of over-cook in the existing batch steam process. Recommendations are made for improving and speeding up the cooking process. The last two models are modifications of the nonlinear moisture penetration model 2. above. The results of these improved models have the potential to provide finer adjustments to estimates of wetting times. 3. A cereal grain swells significantly during wetting. A model that takes this into account is developed and solved approximately. 4. Another wetting model describes the effect of the gelatinisation reaction, slowing moisture penetration, and leading to a sharp front entering the grain. The effect of gelatinisation on the speed of moisture penetration is expected to be more important for the present high-temperature cooking process, than when soaking a grain at a lower temperature. This model is also developed and solved approximately

Characterisation of food fibres and their effect on starch digestion in an in-vitro system at physiological shear rates : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Anatomy and Physiology at Massey University, New Zealand

Material removed from thesis for copyright reasons: Appendix 5 - Hardacre, A.K., Yap, S-Y., Lentle, R.G., Janssen, P.W.M., & Monro, J.A. (2014). The partitioning of water in aggregates of undigested and digested dietary particles, Food Chemistry, 142, 446-454. https://doi.org/10.1016/j.foodchem.2013.07.063 Appendix 6 - Hardacre, A.K., Yap, S-Y., Lentle, R.G., & Monro, J.A. (2015). The effect of fibre and gelatinised starch type on amylolysis and apparent viscosity during in vitro digestion at a physiological shear rate, Carbohydrate Polymers, 123, 80-88. https://doi.org/10.1016/j.carbpol.2015.01.013 Appendix 7 - Hardacre, A.K., Lentle, R.G., Yap, S-Y., & Monro, J.A. (2016). Does viscosity or structure govern the rate at which starch granules are digested? Carbohydrate Polymers, 136, 667-675. https://doi.org/10.1016/j.carbpol.2015.08.060The fast pace of life promotes the excessive consumption of processed starchy food containing high levels of sugar, salt and oil; which can increase the prevalence of type II diabetes, colon and cardiovascular diseases. The addition of dietary fibres in the diet increases the viscosity of digesta, delays mixing in the gut, and promotes laxation. However, few studies attempt to quantify the possible physical and chemical effects of either soluble (food gums) and insoluble (largely cellulose) fibre in the diet. These effects may encompass the retention of water inside the fibre particles, between particles in the fibre mass and direct effects of the chemical nature of the fibre on the digestion process. In this study, the fractions of water held in the various partitions of insoluble particulate dietary fibres are quantified. The relationship between the volume fraction of soluble and insoluble dietary fibres in simulated digesta at physiological concentrations and the rheological properties of the suspension at physiological shear rates is determined. Furthermore, the impact of fibre and shear rates on the digestion of starch in-vitro at physiological shear rates was measured. This work provides the first quantitative assessment of the effects of the physical attributes of dietary fibre on the digestion of starch in-vitro, at physiological shear rates. In this work, four insoluble fibre types were used to construct aqueous suspensions containing solid volume fractions similar to those of pig digesta from the small intestine; these suspensions also were shown to have similar rheological properties to those of pig digesta at physiological shear rates. In addition, a soluble fibre (Guar gum) was used to construct solutions with viscosities comparable to those of the particulate suspensions. Gelatinised and partially gelatinised starch was added to these suspensions and its rate of digestion at 37°C under simulated small intestinal conditions was measured at shear rates covering the reported physiological range. Important results from this work include: - The proportion of water retained by a given volume of hydrated mass of large fibre particles (AllBran®) was double that of smaller particles (wheat fibre). For all of the solid particles used, the proportion of water sequestered by the intra-particulate voids was less than 4% of the volume of the particles, similar proportions were determined for indigestible particles recovered from the colon of pigs and from human faeces. - Food fibre systems containing less than 20% by volume (solid volume fraction, φ = 0.20) of insoluble dietary fibres showed Newtonian rheological properties and the viscosity of these suspensions could be predicted from φ by the Maron-Pierce model. Starch/fibre suspensions prepared with φ below 20% (φ = 0.68-0.98) had a similar viscosity to that of starch/guar suspension comprising 10% (w/v) starch and 0.4% (w/v) guar. During in-vitro digestion, the viscosity of the starch/fibre suspensions decreased logarithmically over the first 20 minutes during which about 30% of the starch was hydrolysed, this was followed by a prolonged period of slow digestion as the slowly digested starch (SDS) and resistant starch (RS) were hydrolysed. The rate of starch digestion was independent of the type of insoluble fibre and was not affected by suspension viscosities used providing shear rates could be maintained within physiological levels. For guar, rates of digestion were slowed probably due to non-competitive inhibition of the amylase by the guar. - When shear rates were below the physiological range (0.1 s-1) or gelatinisation was incomplete, the rate of digestion became linear over the first 20 minutes of digestion suggesting that the rate of digestion was limited by transport processes at low shear in viscous suspensions. - This study provides useful information regarding the limiting concentration of particles and hence viscosity of digesta in the gut if rates of digestion are to be maximised. Additionally, it is suggested that guar, even at low concentration may reduce glycemia by reducing rates of amylolysis

Factors affecting sorghum protein digestibility

In the semi-arid tropics worldwide, sorghum (Sorghum bicolor (L.) Moench) is cultivated by farmers on a subsistence level and consumed as food by humans. A nutritional limitation to its use is the poor digestibility of sorghum protein when wet cooked. The factors affecting wet cooked sorghum protein digestibility may be categorised into two main groups: exogenous factors (grain organisational structure, polyphenols, phytic acid, starch and non-starch polysaccharides) and endogenous factors (disulphide and non-disulphide crosslinking, kafirin hydrophobicity and changes in protein secondary structure). All these factors have been shown to influence sorghum protein digestibility. More than one factor may be at play at any time depending on the nature or the state in which the sorghum grain is; that is whether whole grain, endosperm, protein body preparation, high-tannin or condensed-tannin-free. It is proposed that protein crosslinking may be the greatest factor that influences sorghum protein digestibility. This may be between ?- and ß-kafirin proteins at the protein body periphery, which may impede digestion of the centrally located major storage protein, a-kafirin, or between ?- or ß-kafirin and a-kafiri

Macromolecular interactions during gelatinisation and retrogradation in starch-whey systems as studied by rapid visco-analyser

Gelatinisation and retrogradation of starch-whey mixtures were studied in water (pH 7) using the Rapid Visco-Analyser (RVA). The starch:whey ratios ranged from 0:100 - 100:0. Wheat starch, and whey protein concentrate (about 80% solids basis) and isolate (about 96% solids basis) were used. Mixtures with whey isolates were generally more viscous than those with whey concentrates, and this was attributed to fewer non-protein milk components in the former. Whey protein concentrates and isolates reduced the peak, trough and final viscosities of the mixtures, but the breakdown and setback ratios of the mixtures were increased. The gelatinisation temperature increased with whey substitutions indicating that whey protein delayed starch gelatinisation. The temperature of fastest viscosity development decreased as the amount of whey was increased. Whey protein isolate generally exercised a lesser effect than the concentrate. At between 40 - 50% whey substitutions, the dominant phase changed from starch to protein irrespective of the source of the whey protein. An additive law poorly defined selected RVA parameters. Both macromolecules interacted to define the viscosity of the mixture, and an exponential model predicted the viscosity better than the additive law. The results obtained in this study are discussed to assist the understanding of extrusion processing of starch-whey systems as models for whey-fortified snack and ready-to-eat foods. Copyright ©2006 The Berkeley Electronic Press. All rights reserved

A comparison of the kinetics of in vitro starch digestion in smooth and wrinkled peas by porcine pancreatic alpha-amylase

This study describes the impact of crop genetics and processing in two pea lines (Pisum sativum L.) on starch digestion kinetics. Mutation at the rugosus (r) locus leads to wrinkled pea seeds, a reduction in starch content and a lower extent of in vitro starch digestibility. The Logarithm of Slope (LOS) kinetic model was used to analyse digestion curves obtained using porcine pancreatic α-amylase for a range of particle size fractions. Changes in starch structure induced by the r mutation led to clear differences in starch digestion kinetics for purified starches and pea flours. Larger particle size fractions showed slowed starch digestion relative to the purified starch, but significant differences still existed between r and wild type pea lines. It is expected that this work will help inform the design of future studies where both starch structure and food structure are important determinants of digestion behavior

Improving efficiency of pig feed manufacturing and application of additives

The project has demonstrated that processed feeds with similar ingredient mixtures differ widely between mills in throughput, energy use, pellet hardness and durability and nutritional quality for growing pigs. Preparation of grains before mixing, specific ingredients and additives used as well as the physical structure of the processing units all affect the cost of manufacture and physical and nutritional quality of the finished product

Effect of Fish Proteins, Salt, Sugar and Monosodium Glutamate on the Microstructural, Rheological and Physico-Chemical Properties of Fish Cracker ('Keropok')

Fish cracker or more commonly known as 'keropok' in Malaysia is a popular snack food among countries in the ASEAN region. This work examines factors affecting 'keropok' quality such as the effect of fish proteins, salt. sugar, monosodium glutamate (MSG) on the gelatinisation of tapioca and sago st arches. Microstructural studies of 'keropok' during different stages of processing were al so observed and correlated to rheological behaviour. Results from differential scanning calorimetry (DSC) showed that with increasing fish content the conclusion gelatinisation temperature (Tc) of the mixture remained relatively constant while the range of gelatinisation temperature decreased. There were hardly any effect due to the addition of 1% sugar and 0.4% MSG. on the onset (To) and peak(Tp) gelatinisation temperatures of sago and tapioca starches. The addition of 2% salt had the greatest effect on gelatinisation temperature of 'keropok' mixture, linear expansion of fried'keropok',and small and large deformations of 'keropok' gel. The technology of producing a good expanded 'k that fresh fish, sufficient amount of salt (2% of the total weight of wet fish and starch), proper sequence of mixing of the 'keropok' mixture to form evenly distributed fiexpansion, full gelatinisation of fish-starch gel, and elastic fish-starch gel formation. At high fish contents (60-70%) the formation of fish protein network in the matrix caused a drop in expansion. There was, however, a sharp increase in the compressive strength of the 'keropok' gel. This result is complemented by the higher storage modulus (G') and lower loss tangent (tan ᵟ) values obtained, indicative of the existence of a strong elastic network. Such conditions were observed when the microstructure of the fish muscle fibres appeared to be well crosslinked. The findings in this study revealed that in order to produce better expanded 'keropok' and a more elastic and fully gelatinised 'keropok' gel, superior interms of appearance, shape and linear expansion, several important factors that ensure even distribution of fish proteins in the fish-starch gel must be taken into account. In conclusion, fresh fish, sufficient amount of salt (2% of the weight of wet fish and starch) and the proper sequence of adding ingredients in mixing are recommended to produce high quality ' keropok'

Efekti hemijskih promena skroba i proteina na fizicke osobine peleta u odnosu na tehnologiju ekstrudiranja

Termalna obrada stočne hrane utiče i pozitivno i negativno na dostupnost glavnih nutrijenata hrane, a od posebnog je značaja u slučaju skroba i proteina. Prilikom obrade stočne hrane skrob i proteini su izloženi jedinstvenim i nepovratnim hemijskim modifikacijama. Ove modifikacije uključuju promene u molekularnoj strukturi kroz procese želatinizacije skroba, odnosno denaturacije proteina i mogu da rezultuju u povoljnim funkcionalnim osobinama odnosno nutritivnim vrednostima pomenutih komponenti. Međutim, pregrevanje stočne hrane prilkom termalne obrade vodi do degradacije skroba i proteina praćeno formiranjem novih kompleksa među komponentama hrane, što na kraju rezultuje negativnim nutritivnim vrednostima. Namera iznetog rada je ustanovljenje generalnih međusobnih odnosa između proizvodnih faktora koji karakteristišu termalnu obradu stočne hrane i hemijskih modifikacija skroba i proteina, kao i njihovog pratećeg uticaja na fizički kvalitet peleta