Binding of aroma compounds with legumin. III. Thermodynamics of competitive binding of aroma compounds with 11S globulin depending on the structure of aroma compounds

This paper considers the prominent features in competitive binding of aroma esters from their mixtures to 11S globulin of broad beans (legumin) in aqueous medium at pH 7.2 and ionic strength of 0.05 mol dm⁻³. Series of alkyl acetates (C₄–C₈) and methyl esters of carbonic acids (C₅–C₉), differing in the length of hydrocarbon chain, have been under our studying. To accomplish the ends of the study, a combination of ultrafiltration and gas–liquid chromatography (GC) has been used. An increase in the length of hydrocarbon chain of the aroma esters brought about greater binding affinity for the protein, the occurrence of some structural restrictions in the interior of the protein molecule, preventing binding, and the change in the binding mechanism of the aroma compounds at the specific critical length of hydrocarbon chain. Differential scanning microcalorimetry data suggested that the revealed changes in the binding mechanism of the studied aroma compounds were attributable to the conformational modification of the protein globule as a result of binding with the aroma compounds. A distinguishing feature in binding of methyl esters of carbonic acids with legumin was their greater binding affinity for the protein as compared with alkyl acetates. The mutual effect of aroma compounds on binding from their equimolar mixtures to the protein made itself evident, firstly, as a drastic increase in the binding extent of aroma esters, having rather long hydrocarbon chain and, secondly, as a dramatic change in the binding mechanism of the aroma esters with relatively short hydrocarbon chain.     

Oxidatively induced chemical changes and interactions of mixed myosin, β‐lactoglobulin and soy 7S globulin

The effects of oxidation on the chemical characteristics of myosin, β‐lactoglobulin and soy 7S globulin were investigated in a free radical‐generating system (FeCl₃/H₂O₂/ascorbate). Oxidised myosin exhibited a marked increase (>10‐fold) in carbonyls, a small increase in amines and conversion of some free sulphhydryls to disulphide bonds. Oxidised β‐lactoglobulin and 7S globulin also showed a major increase in the carbonyl content (five‐ and threefold respectively), but other chemical changes were relatively minor. In the oxidised myosin/β‐lactoglobulin composites, some cross‐linked aggregates were formed. Aggregation was also evidenced in the myosin/7S globulin composites exposed to the oxidising agents. The results indicated that oxidation enhanced interactions of the non‐muscle proteins with myosin apparently through the modification of amino acid side chains. These physicochemical changes may influence the functionality of processed muscle foods. © 2000 Society of Chemical Industry     

Interaction of Lupinus angustifolius L. α and γ conglutins with 13-hydroperoxide-11,9-octadecadienoic acid

Food proteins suffer losses of functional and nutritional value due to reaction with lipid peroxidation products. The seed globulins conglutin α and γ from Lupinus angustifolius L. have been incubated with 13-hydroperoxide-11,9-octadecadienoic acid at pH 9 as a model of the interactions between seed storage proteins and lipid peroxidation products during storage and processing of protein-based products. The incubation lead to fragmentation and/or polymerization of the conglutins as determined by chromatographic and electrophoretic analysis. Losses of tryptophan, methionine, cysteine, proline, valine and leucine were shown by amino acid analysis. In vitro digestibility assays did not show clear differences between the digestibilities of the native conglutins before and after incubation with the hydroperoxide. Nevertheless, it is concluded that reaction with 13-hydroperoxide-11,9-octadecadienoic acid lead to a decrease in the nutritional value of the conglutins because the losses of essential amino acids were substantial. In addition, fragmentation and polymerization reactions most likely have a detrimental effect in the functional properties of the conglutins. These results highlight the deleterious effects that lipid peroxidation products have on products such as protein concentrates, isolates and hydrolysates obtained from lipid-rich seeds.     

Heat-adaptation induced thermotolerance in Staphylococcus aureus: Influence of the alternative factor σ

The role of σ^B in the Staphylococcus aureus heat-shock induced thermotolerance was investigated. Survival curves at 58 °C of S. aureus strain Newman and its isogenic ΔsigB mutant were obtained for native and heat-shocked cells (45 °C for 5–120 min) in exponential and stationary phase of growth. The magnitude of the acquisition of thermotolerance at 58 °C depended on the growth phase and on the duration of the heat shock. Stationary growth phase cells were always more heat tolerant than exponentially growing cells and thermotolerance increased with heat-shock duration up to 120 min. S. aureus cells were able to increase their heat tolerance in the absence of the σ^B factor. In stationary phase, whereas in the parental strain the thermotolerance was increased by a factor of 12 after a heat shock of 120 min at 45 °C (δ values at 58 °C for native and heat-shocked cells were 0.63 and 7.22 min, respectively), in the mutant strain it increased 43 fold (δ values 0.09 and 3.87 min). The addition of chloramphenicol to the adaptation medium resulted in a lower increase in heat tolerance but did not prevent it completely, suggesting that S. aureus can partially increase its thermotolerance without “de novo” protein synthesis. Both the number of non-damaged cells and the proportion of cells able to repair sublethal damage were higher for heat-shocked cells.     

Effects of different food commodities on larval development and α-amylase activity of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

The present work was undertaken to study the influence of four commodities (wheat flour, dates, sorghum and barley) on Plodia interpunctella post-embryonic development. Larval weight, larval mortality, pupation and adult emergence were recorded. The study also aimed to find out the effect of these commodities on protein and glycogen production as well as on α-amylase activity. Results indicated that the weight of fourth instar larvae placed on dates increased gradually. Percentage mortality was low. Pupation and adult emergence were delayed. In contrast, the weight of larvae placed on wheat flour, sorghum or barley remained low. Pupation and adult emergence occurred sooner than among those placed on dates and the percentage mortality was highest for larvae placed on barley. Results also showed that protein content and α-amylase activity were lower for larvae placed on dates than for those placed on other commodities. The biochemical composition of different commodities showed that dates are a rich source of glucose, while their protein and starch contents were very low as compared to the other commodities. In contrast, wheat flour, sorghum and barley contained large amounts of starch and protein and low amounts of glucose. Thus, the reduction in α-amylase activity was probably due to the high levels of glucose in dates.     

Towards a better understanding of the relationship between the β-carotene in vitro bio-accessibility and pectin structural changes: A case study on carrots

The quality of fruit and vegetables based products is affected by processing. Two important parameters to consider are the structural characteristics and the nutritional value. As pectin is a major constituent of plant cell walls, pectin structure engineering can be used as a tool to affect the structural quality of plant based food products. During thermal processing, pectin characteristics are influenced. Recently, it has been highlighted that nutrient bio-accessibility is affected by food structure. The intracellular localization of nutrients implies that their accessibility can be hindered by several structural elements.Therefore, this investigation focused on the relation between the structural quality and the nutritional value of carrots. Texture was measured as an indication for the structural quality, while the β-carotene in vitro bio-accessibility was selected as a parameter reflecting the nutritional value. The effect of thermal (pre)processing on this relationship was investigated. The results clearly indicate that the structural quality of carrots and the β-carotene in vitro bio-accessibility are inversely correlated. Moreover, it was hypothesized that pectin changes during thermal processing play a key role in this inverse relationship.