Pineapple wastes: A potential source for bromelain extraction

This study investigates the isolation and characterization of bromelain extract from the wastes of Nang Lae and Phu Lae pineapple cultivars (economical fruits of Chiang Rai province, Thailand). The waste portions such as the peel, core, stem and crown were 29–40%, 9–10%, 2–5% and 2–4% (w/w), respectively. The extract of crown from both cultivars gave the highest proteolytic activity and protein contents, while the extract from the stem exhibited the lowest values. SDS–PAGE showed that the major protein band in the extracts was ～28 kDa. Activity staining of the crown extracts from both cultivars confirmed that the major protein band showed caseinolytic activity on the casein substrate-gel. All of the crude extracts from both cultivars gave high caseinolytic activity (>80% relative) in a board pH range (3–9). The optimum temperatures for all crude extracts were about 50–60 °C. This study founded that there is much added value into local Thailand pineapple wastes because of bromelain extraction.     

Effectiveness of ethanolic galangal extract (Alpinia galanga Linn.) on inhibition of lipid oxidation in fish muscle systems

Effectiveness of ethanolic galangal extract as an antioxidant in fish mince and fillet was investigated. The extract (5.8 μm gallic acid equivalent; GAE) reduced deoxygenation of sea bass haemoglobin (Lates calcarifer) at pH 6.5. The lag time for TBARs development in washed sea bass mince mediated by the haemoglobin at pH 6.5 was extended from 2 to 8 days by added galangal extract (0.02% w/w GAE). Washing the sea bass fillet with low preformed lipid hydroperoxide (LHP) content by galangal extract solution (0.2% w/v GAE) effectively inhibited the TBARs formation throughout the storage. However, in the longtail tuna fillet (Thunnus tonggol) having a significant content of preformed LHP, there was nonsignificant difference in the reaction lag time of the samples washed with the solution and with water. Thus, galangal extract can be used as an antioxidant in fish if its application is performed before initiation of lipid oxidation.     

Effect of Sodium Chloride and Osmotic Dehydration on Viscoelastic Properties and Thermal-Induced Transitions of Duck Egg Yolk

The effects of NaCl and osmotic dehydration on the linear viscoelastic behavior of duck egg yolk were evaluated. An increase in NaCl concentrations from 0% to 3.0% (w/w) resulted in a remarkable change in the linear viscoelastic behavior by inducing a sol–gel transition, specifically. The transition was more pronounced when 1.5% (w/w) NaCl was incorporated. The effect of dehydration on aggregation and network formation was predominant than that of the NaCl addition. Nevertheless, at a lower degree of dehydration, the addition of NaCl could modulate the viscoelastic behavior of duck egg yolk, resulting in a well-developed gel network. Addition of NaCl into duck egg yolk could stabilize the protein molecules as evidenced by an increase in denaturation temperature as well as a delay in gel network formation. As visualized by a scanning electron microscope, the denser network with smaller voids was observed in duck egg yolk gel with increasing NaCl concentration and degree of dehydration.     

Linear and non-linear viscoelastic behaviors of crosslinked tapioca starch/polysaccharide systems

Effects of polysaccharides on both the thickening performance and large deformation behavior of mixtures of various crosslinked tapioca starch and polysaccharide were investigated. It was found that the gelatinized crosslinked tapioca starch at 1-8% w/w in aqueous solutions behaved as swollen granules with the low-shear viscosity described by Krieger & Dougherty equation. To achieve thickening performance, 3.5% w/w starch was cooked with a range of 0.5% w/w polysaccharides, i.e. konjac glucomannan, guar gum, xanthan gum, and their 50:50 mixtures. It was shown that additions of polysaccharides greatly affected the rheological behavior of the suspensions, predominantly in the linear viscoelastic regime. The studied mixtures of starch and polysaccharides exhibited strong synergistic effects as evidenced from the increase in their consistency coefficients and the excess storage moduli calculated from the Palierne equation. Moreover, the mixtures containing xanthan gum showed weak-gel characteristics while the others demonstrated liquid-like behavior. In the non-linear viscoelastic analysis, arrangement of starch granules and specific interfacial interactions evidently affected the deformation behavior of the mixtures of crosslinked tapioca starch and polysaccharide. The mixture of konjac glucomannan and xanthan also largely improved stress susceptibility of the suspension and gave the unique shear stiffening under large amplitude oscillatory shear experiment.     

A mechanistic approach to extract the mechanical properties of individual constituents in plasma-sprayed metal matrix composite coatings

A mechanistic approach to determine the in-situ properties of individual constituents in a plasma sprayed metal matrix composite (MMC) coating was proposed. The approach was based on micro-indentation and inverse analysis techniques. Utilising the indentation data obtained from the micro-indentation experiments, elastic moduli of each constituent were calculated using a well-established method whereas yield strength and hardening exponent were extracted using the inverse procedure based on finite element analysis. Finite element results gave a satisfactory agreement between the numerically simulated and the measured indentation load-depth curves. Further studies using three dimensional finite element analyses of Vickers indentation on the MMC coating based on its actual microstructure also showed that the indentation behaviour of the MMC coatings is strongly dependent on its morphology, volume fraction, size and distribution of the reinforcing phase.     

Hydrolysis of surimi wastewater for production of transglutaminase by Enterobacter sp. C2361 and Providencia sp. C1112

Surimi wastewater (SWW) is an industrial wastewater, released during the washing step of surimi preparation from minced fish, that causes environmental problem. In this study, SWW produced from ornate threadfin bream (Nemipterus hexodon) was hydrolysed and used to cultivate Enterobacter sp. C2361 and Providencia sp. C1112 for the production of microbial transglutaminase (MTGase, EC 2.3.2.13). The SWW was repeatedly used to wash the fish mince that gained a final protein content of 3.20% (w/v). The commercial protease, Delvolase was the most appropriate protease used to produce fish protein hydrolysate (FPH) from SWW. The FPH at 40% degree of hydrolysis was used instead of a peptone portion in the SPY medium (3.0% starch, 2.0% peptone, 0.2% yeast extract, 0.2% MgSO(4), 0.2% K(2)HPO(4) and 0.2% KH(2)HPO(4), pH 7.0) to cultivate the tested strains at 37°C, shaking speed at 150rpm. Providencia sp. C1112 produced higher MTGase activity (1.78±0.05U/ml) than Streptoverticillium mobaraense (1.61±0.02U/ml) at 18h of cultivation in FPH medium. On the other hand, the Enterobacter sp. C2361 produced lower MTGase activity (1.18±0.03U/ml).     

Effects of cross-linked tapioca starches on batter viscosity and oil absorption in deep-fried breaded chicken strips

In this study, the effectiveness and feasibility of using various degrees of cross-linked tapioca starches in batter and breading formulations to reduce oil absorptions in deep fried chickens were investigated. Shear flow behaviour, water retention capacity (WRC), pick-up as well as cooked yield of the prepared batters were also examined. Flow curves showed that all studied batters were pseudoplastic, i.e. having shear thinning characteristics. In addition, it was found that the substitution of 20% (w/w) cross-linked starches for wheat flour in the batter formulation significantly reduced the consistency index and WRC of the batters. However, batter pick-up and cooked yield values were insignificantly affected. Oil uptake of fried chicken crusts was determined using differential scanning calorimetry due to its specific advantages over the conventional solvent extraction method. In comparison to the control (wheat) formulation, crusts of fried chicken samples obtained from the formulations containing 20% (w/w) cross-linked starch showed significantly lower oil content by at least 17% relative oil reduction. The highest relative oil reduction was found in the batter containing the highly cross-linked tapioca starch. Furthermore, an increase in water content in the batter formulations resulted in a reduction in the batter pick-up, cooked yield and oil absorption. The degree of cross-linking which in turn resulted in the limited starch granule disintegration is the predominant factor in the reduction of oil content for deep-fried battered food.     

Aqueous two-phase extraction of bromelain from pineapple peels (‘Phu Lae’ cultv.) and its biochemical properties

This study examines the extraction of bromelain from pineapple peels by using an aqueous two-phase system (ATPS). Bromelain from the crude extract predominantly partitioned to the polyethylene glycol rich phase. The best condition for bromelain partitioning was found to be 18% PEG6000-17% MgSO₄, which increased purity 3.44-fold with an activity recovery of 206%. Protein patterns and activity staining showed the molecular weight of bromelain to be about 29 kDa. The bromelain showed the highest relative activity at pH 8.0 and at 60°C. When increasing NaCl concentrations (up to 1.5%, w/v), its activity continuously decreased. The bromelain (0–0.3 units) was applied to hydrolyze collagen. The β, α₁, α₂ components of collagen extensively degraded into small peptides when treated with the bromelain. This study showed that the ATPS can be employed to isolate the bromelain from pineapple peels and the bromelain extract could be used as a meat tenderizing agent.     

On the effect of substrate properties on the indentation behaviour of coated systems

The indentation behaviour of an elastoplastic coating–substrate system is investigated using a combination of dimensional and finite element analyses. Scaling functions relating the indentation load–depth curves to coating and substrate mechanical properties are given. Based on these scaling functions, the indentation behaviour of various coated systems is examined. The critical indentation depth to coating thickness ratio below which the substrate material has a negligible effect on the indentation response of the coated system is identified for various generic coating–substrate systems. Such ratio is given in terms of the yield strength and Young’s modulus of the coating and substrate, i.e. σ_yc/σ_ys and E_c/E_s. The results of parametric studies revealed that the commonly used rule that the maximum indentation depth should be less than 10% of the coating thickness, is applicable only when σ_yc/σ_ys<10. However, indentation experiments should be carried out up to a maximum depth of 5% of the film thickness to avoid any influence from the substrate when σ_yc/σ_ys≥10 and E_c/E_s>0.1.     

Effect of Freezing Rate and Starch Granular Morphology on Ice Formation and Non-Freezable Water Content of Flour and Starch Gels

Ice formation and non-freezable water (W_NFW) of rice flour and tapioca starch gels were studied at two different freezing rates (–10 and –100°C/min) using differential scanning calorimetry. Ice crystal growth was observed in the slow freezing but not in the fast one. Ice melting enthalpies, however, were similar since more ice formed in holding and reheating steps. Melting enthalpy of fully gelatinized systems with water contents ~ 0.50–0.66 was associated to starch composition and granule morphology. Highly swollen tapioca starch gave the lowest enthalpy and the highest W_NFW (0.40 g/g dry starch versus 0.32 and 0.38 g/g dry starch of normal and waxy rice flours, respectively). The further studies revealed that the W_NFW values were associated to swelling power, solubility, and granule morphology.