Storage quality of pineapple juice non-thermally pasteurized and clarified by microfiltration

Microfiltration (MF) is classified as a non-thermal process for the fruit juice industry. It could provide a better preservation of the phytochemical property and flavor of the juice. This work aimed to study the stability of phytochemical properties including vitamin C, total phenolic content, antioxidant capacity (2-Diphenly-1-picrylhydrazyl: DPPH, free radical scavenging capacity and Oxygen Radical Absorbance Capacity: ORAC assays), microbial and chemical–physical (color, browning index, pH and total soluble solid) properties of MF-clarified pineapple juice during storage at various temperatures (i.e. 4, 27, and 37 °C). The juices were clarified by microfiltration using hollow fiber module. The results showed that most of the phytochemical properties and soluble components were retained in the juice after microfiltration. No microbial growth was detected after 6 months of storage. The storage time and temperature did not affect total soluble solids and pH (P > 0.05). The color (L^*) of clarified juice stored at 4 °C was lighter than the juices stored at higher temperature levels (P < 0.05). The phytochemical properties and total phenol content of the juice significantly decreased as storage time and temperature increased (P < 0.05). Vitamin C content was the attribute that affected storage time and temperature most as indicated by reaction rate constant and activated energy. Storage of non-thermally pasteurized and clarified pineapple juice at 4 °C was the most suitable since it allowed the best quality preservation.     

Influence of gas sparging on clarification of pineapple wine by microfiltration

A microfiltration process with a tubular ceramic membrane was applied for clarification of pineapple wine. The process was operated with the membrane pore size of 0.2 μm at transmembrane pressure of 2 bar and crossflow velocity of 2.0 m/s. The effects of gas sparging on permeate flux, fouling and quality of clarified wine were studied. It was found that a relatively low gas sparging rate could increase permeate flux up to 138%. Further increase of the gas sparging rate did not improve permeate flux compared with that without gas sparging. Gas sparging affected the density of cake layer. Increasing gas sparging rate led to an increase in specific cake resistance. It was observed that increasing gas sparging rate could reduce reversible fouling rather than irreversible fouling. The turbidity of pineapple wine was reduced and a clear product with bright yellow color was obtained after microfiltration. The negative effect of gas sparging which caused a loss of alcohol content in the wine was also observed.     

Effect of membrane property and operating conditions on phytochemical properties and permeate flux during clarification of pineapple juice

The effects of membrane property on the permeate flux, membrane fouling and quality of clarified pineapple juice were studied. Both microfiltration (membrane pore size of 0.1 and 0.2 μm) and ultrafiltration (membrane molecular weight cut-off (MWCO) of 30 and 100 kDa) membranes were employed. Membrane filtration did not have significant effects on the pH, reducing sugar and acidity of clarified juice whereas the suspended solids and microorganism were completely removed. The 0.2 μm membrane gave the highest permeate flux, total vitamin C content, total phenolic content and antioxidant capacity as well as the highest value of irreversible fouling. Based on these results, the membrane with pore size of 0.2 μm was considered to be the most suitable membrane for the clarification of pineapple juice. The optimum operating conditions for the clarification pineapple juice by membrane filtration was a cross-flow velocity of 3.4 ms⁻¹ and transmembrane pressure (TMP) of 0.7 bar. An average flux of about 37 lm⁻² h⁻¹ was obtained during the microfiltration of pineapple juice under the optimum conditions using batch concentration mode.     

Secretion of heterologous and native proteins,growth and morphology in batch cultures of Aspergillus niger B1‐D at varying agitation rates

The influence of bioreactor operational conditions on the micromorphology of batch cultures of Aspergillus niger B1‐D, containing a hen egg white lysozome (HEWL) marker protein, was examined using computerised image analysis. Significant differences in micromorphology were observed with increased stirrer speed, with shorter organisms with shorter hyphal elements occurring as agitation speed increased, even though mean tip numbers were similar. This may explain the observed increase in the total extracellular protein, since the ratio of synthetic (tip) to non‐synthetic zones became increasingly favourable. HEWL concentrations fell above 500 rpm, probably due to the effects of DOT (dissolved oxygen tension) on the glucoamylase HEWL fusion. HEWL was susceptible to proteolytic degradation, by native proteases, during the autolytic phase. Such insights may indicate why a gene from one mould expressed in a close relative can give production levels equivalent to levels of native enzymes, while secretion of a gene from a ‘distant’ source, eg a higher eukaryotic gene, occurs at much lower levels. © 1999 Society of Chemical Industry