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.     

The mechanical properties of model-compacted tablets

In this study, the compressive strength of tablets made with salt, starch and fat was investigated. The strength was found to increase with compaction pressure, up to a maximum value where further increase in the compaction pressure led to no increase in the strength. The maximum strength corresponded to the point where zero porosity was obtained during the compaction process. However, because of the elastic rebound of the tablets after ejection, the maximum strength corresponded to non-zero final tablet porosities which varied between the materials. For this reason, the use of the density occurring during the compaction process appeared to provide a more reliable comparison between the materials. A simple linear mixing rule did not hold in characterising the strength in the salt:starch:fat systems. However, two regimes were observed depending on the salt volume fraction. At low salt volume fractions, the effect of the salt was negligible. After a certain critical salt volume fraction, increasing the salt led to an increase in the strength. Finite element simulations based on X-ray microtomography images of the tablets suggested that in the first regime, the stresses due to the salt particles were localised but in the second regime, stress-bearing networks were formed between the salt particles.

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Determination of large deformation and fracture behaviour of starch gels from conventional and wire cutting experiments

Large deformation and fracture properties of two types of starch gels were investigated through uniaxial compression, single edge-notched bend (SENB) and wire cutting experiments. Tests were performed at various loading rates and for various starch/powder concentrations (%w/w). It was found that starch gels exhibit rate independent stress–strain behaviour but show rate-dependent fracture behaviour, i.e. stress–strain curves at three loading rates are similar but fracture stress and fracture strain increase with increasing strain rate. This is rather unusual and interesting behaviour. SENB and wire cutting experiments also revealed rate-dependent fracture behaviour and that the true fracture toughness (G _c) values increase with loading/cutting speeds and starch powder concentration. In addition, the G _c values from wire cutting and SENB tests were in reasonable agreement. The wire cutting process was also studied numerically using finite element techniques. A non-linear elastic constitutive relationship based on Ogden was used to model the starch gels and a frictionless condition was assumed at the wire–starch gel contact interface. A fracture criterion based on maximum principal strain was assumed for the prediction of the steady state cutting force.     

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.     

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.     

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.     

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).     

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.     

Physicochemical and rheological characteristics of commercial chili sauces as thickened by modified starch or modified starch/xanthan mixture

Physicochemical and rheological properties of various commercial chili sauces were characterised in this study. It was found that all studied sauces were acidic. Fourier transform infrared spectroscopy and colour staining experiments showed that the studied sauce could be categorised into two groups: one containing only starch and the others having both starch and xanthan within their ingredients. The rheological measurements showed that all sauces had a weak gel-like characteristic with strong shear thinning behaviour. In particular, the sauce with the weakest network contained only starch. Flow experimental data, fitted with the Herschel-Bulkley model, also revealed that the sauce with the lowest total solid content had undetectable yield stress, the lowest consistency coefficient, and the highest flow behaviour index, hence the weakest network structure amongst the studied sauces. The xanthan-starch mixture was shown to be beneficial as they could interact synergistically in acidic condition to enhance the gel-like characteristics and shear thinning behaviour of chili sauces.