Massey Documents by Type

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Effects of Spray-Drying and Freeze-Drying on Bioactive and Volatile Compounds of Smoke Powder Food Flavouring
(Springer Nature, 2022-02-23) Xin X; Essien S; Dell K; Woo MW; Baroutian S
Transforming liquid smoke to powder form can provide convenience for use and storage. Liquid smoke was prepared by fast pyrolysis technology using a fluidised bed and converted to smoke powder by spray-drying or freeze-drying processes. Both drying processes effectively retained the bioactive compounds in the powder encapsulates with retention efficiencies up to 80%. The bioactive capacities were approximately two times higher than liquid smoke. Spray-drying did not induce thermal damage to the bioactive compounds, and the dominant compounds were retained in the powders. Gas chromatography–mass spectrometry and principal component analysis indicated that the chemical composition was not significantly changed after both drying methods, but small molecular carbonyls, furans and phenols were partially lost. The spray-dried particles had a spherical shape, while freeze-dried particles had irregular shapes because of different powder preparation methods. The particle size of spray-dried powders was in the range of 6.3 to 6.9 µm, while the value for freeze-dried powders was decreased from 580.4 to 134.7 µm by increasing the maltodextrin concentration. The freeze-dried powders performed better in terms of flowability and cohesiveness because of their relatively high density and large particle size. This study revealed that both encapsulation methods could efficiently prepare smoke powder. Spray-drying process would be suitable for large-scale production, while freeze-drying could be used to optimize the encapsulation efficiency of bioactive compounds.
Impact of protectant uptake on the shelf-life of dried Lacticaseibacillus rhamnosus
(Elsevier, 2022-01) Priour S; Welman A; Singh H; Ellis A
To improve the survival of dried probiotics, it is advised to expose the bacteria to protectants prior to processing, allowing equilibration of internal solutes. However, optimal conditions for this exposure remain unclear. This study examined solute uptake by Lacticaseibacillus rhamnosus HN001 (formally known as Lactobacillus rhamnosus HN001) at 4 °C and 20 °C, over exposure times of 0–240 min. The cells were exposed to hyperosmotic solutions of glucose and sucrose, two potential protective sugars, which are metabolisable and have different molecular weights. Sugar uptake was analysed through HPLC, while the impact on cell viability after freeze-drying was examined at 30 °C and 40 °C. The interactions between cell biomolecules and sugars were examined using Nano DSC. Results showed that the sugars were rapidly taken up by the cells, independent of temperature. At 20 °C, glucose was readily metabolised, eventually resulting in loss of cell viability during storage. Conversely, the Nano DSC study revealed interactions between the cells and sucrose, potentially providing some explanation as to the stability of the cells. In conclusion, sugar type and exposure temperature were shown to exert a significant effect on the viability of Lacticaseibacillus rhamnosus. Nano DSC is a promising technique to understand the protectant and cells’ interactions.
Rate controlling mechanisms in atmospheric freeze drying : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemical and Bioprocess Engineering at Massey University, Manawatū, New Zealand
(Massey University, 2023) Mathew, Merit
Atmospheric freeze drying (AFD) can be considered a cost-effective alternative to vacuum freeze drying (VFD) but the very slow drying rate associated with it limits industrial scale adoption. Nevertheless, there are applications, particularly with thin sections such as sliced fruit or leaves, for which hops is an example, where the rate of AFD is relatively high. Therefore, it is important to understand the rate-controlling mechanisms in AFD and how it is affected by the structure of the fruit or leaf. Such understanding will help identify the bottlenecks of the process and thus the steps that may be taken to overcome them. This project has developed a mathematical model for AFD by considering the intrinsic material properties and the theoretical principles of heat and mass transfer. This could help the end-users to run simulations of AFD for different products and arrive at the best drying strategies to achieve faster drying rates before doing time-consuming and expensive experiments. In this work, hops are considered as the model system for the model development. The study needed high-quality experimental data for continuous in-situ weight loss measurements during AFD and there was a lack of such data in the literature reviewed. To deliver this, part of the project has developed a new experimental apparatus. The experimental apparatus developed is capable of continuous weight-loss measurement and data logging temperature and RH of the air in the drying chamber. Temporal weight-loss trial data are used to fit parameters and predict the drying rate and product weight loss. During the study it was found that AFD of hops is a mass transfer limited process. The drying rate was found to increase with process temperature and the adsorbent to hops ratio. Air circulation also helped in increasing the drying rate. The one-dimensional model developed to simulate AFD of hops was able to predict the drying behaviour based on the process parameters and the fitting factors for the hops. Ice sublimation was also studied in this project, based on the hypothesis that the AFD of hops is a type of pure ice sublimation with an additional layer of resistance to mass transfer. This hypothesis was found to be true for the present case and the model was development based on this.

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