John J. Fitzpatrick

Flow property measurement of food powders and sensitivity of Jenike’s hopper design methodology to the measured values

Abstract The flow properties and powder physical properties were measured for 13 food powders. The flow properties were measured using shear cell techniques, and the powder physical properties measured were particle size, moisture, bulk and particle densities. The flowability of the food powders, as characterised by flow index, varied from easy flow to very cohesive. Particle size and moisture content do affect flowability, however there was no strong relationship for trying to relate the flowability of the food powders based solely on these physical properties. There was no relationship between measured powder physical properties and their wall friction characteristics. As a result, surface forces between the powder particles, and between particles and the wall surface play an important role in determining the flow nature of the powders, and this is an area requiring research. Jenike’s mathematical analysis to determine the minimum hopper angle and opening size for mass flow is the engineering standard practice for designing a hopper. Applying this analysis, using values of the measured food powder flow properties, shows that this can occasionally produce some unexpected values for the hopper opening size.

Characterisation of food powder flowability

This paper presents a characterisation of the flow properties of four food powders (flour, skim-milk, tea and whey-permeate). Physical property measurements, including particle size, bulk and particle densities, water sorption isotherms and DSC thermograms, are presented. Powder flowability was measured using an annular shear cell. The flowability of the 4 food powders are compared and discussed with reference to their physical properties and the relative humidity of the surrounding atmosphere. One application of powder flowability data is in the design of hoppers. Different failure properties from shear tests are calculated for each of the food powders. They are then applied to estimating and comparing the critical hopper dimensions for mass flow for each powder.

Effect of relative humidity and temperature on food powder flowability

This paper presents an evaluation of the influence of relative humidity and temperature on the flowability of the following food powders: flour, tea and whey permeate. These powders were selected because of their different physical properties. Powder flowability was measured using an annular shear cell in a chamber with controlled relative humidity and temperature. A number of powder physical properties, including particle size distribution, water sorption isotherms and differential scanning calorimetry (DSC) thermograms, were measured. These properties are used in interpreting and comparing the flowability measurements for each powder.

Effect of storage time and consolidation on food powder flowability

This paper presents an evaluation of the effect of storage time and consolidation on the flowability of the following food powders: flour, tea and whey permeate. Instantaneous and temporal flow functions of the powders were measured to quantify the combined effects of compression stress and time. The flow functions were measured using a Jenike shear cell and a consolidating bench. A number of powder physical properties, including moisture content, bulk density and particle size were measured. These properties are used in interpreting and comparing the flowability measurements for each powder.

Malt combing nuts as a nutrient supplement to whey permeate for producing lactic by fermentation with Lactobacillus casei

Abstract Malt combing nuts (MCN) is a low value byproduct from the malting industry. It provides a cheap source of nitrogen and vitamins and has potential for being applied as a nutrient supplement in fermentations to produce lactic acid. This work investigates the supplementation of whey permeate with MCN to produce lactic acid by fermentation with Lactobacillus casei , and compares it with fermentations supplemented with yeast extract (YE). The results showed that MCN can be applied successfully as a nutrient supplement to produce lactic acid by fermentation, achieving complete sugar conversion and lactic acid yield similar to YE supplementation. 5% w/v MCN addition was required to achieve a fermentation time of around 55 h in whey permeate containing lactose at a concentration of 55 g/l. This was similar to fermentations with 0.3% w/v YE supplementation. The major advantage of using MCN is that its raw material cost for supplementing a fermentation is many times lower than YE for a comparable fermentation. However, on the other hand, the results showed that the levels of impurities remaining after fermentation are a lot higher. MCN adds much more ash to the fermentation and there is a lot more unused nitrogen remaining at the end of the fermentation. This is undesirable for the production of high purity lactic acid as it leads to increased separation costs.

Influence of whey protein hydrolysate addition to whey permeate batch fermentations for producing lactic acid

Abstract Addition of whey protein hydrolysate (WPH) to whey permeate fermentations, by Lactobacillus helveticus , to produce lactic acid was investigated. Three to four percent (w/w) supplementation with WPH solution (10% w/w protein) was required to obtain high lactose conversion and lactic acid yield in a fermentation time of 30–40 h. At this percentage supplementation, the nitrogen content of the media was 0.06–0.09% w/w. The bacteria used around 0.02% w/w nitrogen during fermentation, thus there was an abundance of unused nitrogen remaining at the end of fermentation. At 3–4% supplementation, it was calculated that around 36–47% of whey protein concentrate produced from whey would be required to supplement the whey permeate fermentation in the form of the hydrolysate.

Effect of manganese on Lactobacillus casei fermentation to produce lactic acid from whey permeate

Batch fermentations were performed to investigate the effect of manganese addition, in the form of MnSO4·H2O, on the performance of Lactobacillus casei for producing L-lactic acid from whey permeate supplemented with yeast extract. There was a particular emphasis on evaluating how little yeast extract and MnSO4·H2O is required while still obtaining high sugar conversion and lactic acid yield, as nutrient supplementation is a raw material cost and can lead to extra residual impurities remaining after fermentation. The addition of MnSO4·H2O had a significant beneficial affect with the fermentation time being reduced from 120 to 24 h for permeate supplemented with 0.50%w:v yeast extract. Fermentations were performed with MnSO4·H2O concentrations in the range of 0.001‐0.03 g:l. From 0.005 to 0.03 g:l, the fermentation performance was very similar, however at the low concentration of 0.001 g:l, the fermentation was significantly slower. With MnSO4·H2O addition, the yeast extract concentration was reduced to 0.30%w:v while still maintaining high sugar conversion and lactic acid yield, however the fermentation was slower at 37 h. At 0.1%w:v yeast extract supplementation, the fermentation performance was poor with only 67% sugar conversion after 150 h of fermentation.

Influence of shear on particle size and fractal dimension of whey protein precipitates: implications for scale-up and centrifugal clarification efficiency

Abstract Whey protein fractionation was carried out at laboratory scale by applying the required temperature and pH conditions in a standard configuration batch agitated vessel to cause selective precipitation and aggregation of proteins. Scale-up of this operation to pilot scale was achieved on the basis of impeller power input per unit volume resulting in similar particle sizes. Separation was subsequently achieved by high-speed disc-stack centrifugation. Processing of precipitates in pumps, valves and at the centrifuge inlet zone can lead to substantial breakage, depending on the strength of the precipitates formed and aged in the batch vessel. Such turbulent processing was mimicked at lab scale by passing the precipitate solution through a ball-valve rig while monitoring the effects on particle size and fractal geometry. Measurement of fractal dimension were used to assess the compactness of precipitates. Precipitates subjected to higher batch vessel impeller shear-rates during formation and ageing were found to be smaller, more compact and better able to resist turbulent breakage and thus should provide better feed–stock for disc-stack centrifugation at pilot scale. Clarification efficiency curves obtained for pilot-scale disc-stack centrifugation confirmed these lab-scale predictions. Recommendations for improved process design in terms of selecting suitable batch vessel shear-rates that ultimately lead to improved separation efficiencies have been made.

Impurity and cost considerations for nutrient supplementation of whey permeate fermentations to produce lactic acid for biodegradable plastics

Abstract A potential application for whey permeate is to ferment it to lactic acid for use in the manufacture of biodegradable plastics. High purity lactic acid is required, thus the separation of impurities after fermentation is a major process cost. For batch fermentations, whey permeate requires nutrient supplementation, which can add to impurity levels at the end of fermentation. This work presents the results of whey permeate fermentations using L. casei , supplemented with yeast extract, whey protein hydrolysate, and malt combing nuts (MCN). There is an emphasis on investigating how little supplement needs to be added while still achieving high lactose conversion and lactic acid yield in a reasonable fermentation time. This was around 0.4% w/w for yeast extract, 5% for the hydrolysate (10% whey protein solution) and 5% for MCN. At these levels of supplement addition, the majority of the supplement is actually not utilised and just contributes to a major increase in the concentration of impurities at the end of the fermentation with a corresponding increase in separation cost, in addition to raw material cost. The ash content of regular whey permeate is another significant source of impurities that need to be separated to produce high purity lactic acid. Fermentations were performed to investigate the effect of low ash content on fermentation performance. Fermentations performed in supplemented demineralised whey permeate, with at least 70% ash reduction, showed no negative effect on fermentation performance, however fermentations conducted in a supplemented lactose solution did show a slowdown in fermentation performance. This is most likely due to mineral deficiency which should not pose a problem as minerals are usually micronutrients, and addition of very small amounts are required to restore fermentation performance.

Investigation of how agitation during precipitation, and subsequent processing affects the particle size distribution and separation of α-lactalbumin enriched whey protein precipitates

Abstract In this work, α-lactalbumin (α-la) rich precipitate particles are formed and aged in a batch stirred-tank from a whey protein concentrate (WPC) dispersion. Precipitation of the proteins occurs during a period of acid-addition followed by an ageing period. This study investigates how stirred-tank impeller agitation and subsequent processing, by means of passing precipitate suspensions through a capillary tube or a partially open ball-valve, affect particle size and composition. Precipitate particles are largely unaffected when subjected to laminar capillary tube flow. However, as flow becomes transitional and thereafter turbulent, particle breakage increases, especially for precipitates formed and aged under mild agitation conditions. Precipitates passed through the ball-valve experience even greater particle size reduction as a sharp geometrical transition results in highly turbulent flow. Moreover, particles formed and aged under low shear conditions, though initially larger, are in fact weaker and fragment to a greater extent during turbulent processing through the ball-valve. This has process design implications for separation processes where particle size is important, as shear history can influence particle toughness. Substantial size reduction of particles can best be mitigated by identifying regions of high turbulence or sudden changes in flow geometry, and by redesigning these regions so as to reduce these effects.