Chemical and Biomolecular Engineering - Research Publications
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ItemThe effect of pH on the fat and protein within cream cheese and their influence on textural and rheological properties(Elsevier BV, 2020-12-01)The effect of variation in acid gel pH during cream cheese production was investigated. The gel microstructure was denser and cheese texture firmer, as the pH decreased from pH 5.0 to pH 4.3, despite the viscoelasticity of these gels remaining similar during heating. Protein hydration and secondary structure appeared to be key factors affecting both cheese microstructure and properties. Proteins within the matrix appeared to swell at pH 5.0, leading to a larger corpuscular structure; greater β-turn structure was also observed by synchrotron-Fourier transform infrared (S-FTIR) microspectroscopy and the cheese was softer. A decrease in pH led to a denser microstructure with increased aggregated β-sheet structure and a firmer cheese. The higher whey protein loss at low pH likely contributed to increased cheese hardness. In summary, controlling the pH of acid gel is important, as this parameter affects proteins in the cheese, their secondary structure and the resulting cream cheese.
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ItemDesign and characterization of casein-whey protein suspensions via the pH-temperature-route for application in extrusion-based 3D-Printing(Elsevier BV, 2021-03)The current interest in individualized food through additive manufacturing has identified a need for more information on the formulation and printability of potential ingredients. Here, the effect of formulation parameters of casein–whey protein suspensions like the pH (4.8–5.4) as well as the casein content (8.0–12.0% (w/w)) mixed with whey protein (2.0–3.0% (w/w)) and the effect of pre-processing parameters including the denaturation of whey proteins (80 °C, 10 min; adjusted pH 6.55, 6.9 and 7.1) on the gel formation via the pH–temperature (T)-route was studied. Rheological measurements showed that the sol–gel transition temperature (G’ = 1 Pa) decreased and the aggregation rate of the casein–whey protein suspensions increased with increasing heating pH value. The aggregation rate was considered to be a key parameter predicting the printability of formulations. By exceeding a certain aggregation rate (250 Pa/10 K), casein–whey protein suspensions were found to be printable resulting in firm and stable gels.
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ItemCharacterising the influence of milk fat towards an application for extrusion-based 3D-printing of casein-whey protein suspensions via the pH-temperature-route(ELSEVIER SCI LTD, 2021-09)This study presents the design and characterisation of casein−whey protein suspensions (8.0/10.0% (w/w) casein and 2.0/2.5% (w/w) whey protein) mixed with dairy fat (1.0, 2.5 and 5.0% (w/w) total fat) processed via the pH−temperature-route in preparation for 3D-printing. Mechanical treatment was applied to significantly decrease the particle size of the milk fat globules and increase surface area, creating small fat globules (<1 μm) covered with proteins, which could act as pseudo protein particles during gelation. Different proteins covered the fat globule surface after mechanical treatment, as a result of differences in the pH adjusted just prior to heating (6.55, 6.9 or 7.1). The protein-fat suspensions appeared similar by transmission electron cryogenic microscopy and the zeta-potential of all particles was unchanged by the heating pH, with a similar charge to the solution (~−20 mV) occurring after acidification (pH 4.8/5.0) at low temperatures (2 °C). A low heating pH (6.55) resulted in increased sol−gel transition temperatures (G՛ = 1 Pa) and a decreased rate of aggregation for protein−fat suspensions. A higher heating pH (6.9 and 7.1) caused an increased rate of aggregation (aggregation rate ≥ 250 Pa/10 K), resulting in materials more promising for application in extrusion-based printing. 3D-printing of formulations into small rectangles, inclusive of a sol−gel transition in a heated nozzle, was conducted to relate the aggregation rate towards printability.
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ItemEffects of shredding on the functionality, microstructure and proteolysis of low-moisture mozzarella cheese(ELSEVIER SCI LTD, 2021-06)Low-moisture mozzarella cheese (LMMC) is commonly shredded before packaging, however, the effects of shredding are not fully understood. Industrially-produced block and shredded LMMC were studied during 8 weeks of storage at 4 °C. Cheese shredded on 15 d and at 8 weeks of age, coated with microcrystalline cellulose and stored in a modified atmosphere (70% N₂ and 30% CO₂), had an altered microstructure after 8 weeks compared with vacuum-packed block cheese. In the latter case the fat formed a more dispersed phase. Proteolysis was higher in shredded samples and a higher level of two bacterial proteases was detected. Despite these differences, the meltability and stretchability of the block and shredded LMMC were similar. The microstructure and functionality of cheese shredded at 15 d and stored for a further 6 weeks was similar to cheese shredded at 8 weeks, suggesting there is a flexible period for performing cheese shredding processes.
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ItemStructure and functionality of almond proteins as a function of pH(ELSEVIER, 2021-10)Almond proteins have potential utility in a range of food and beverages but it is not clear how pH affects protein structure and function. The behaviour of almond protein isolate was examined under conditions of neutral and acidic pH (pH 7 and 4). The isolate was highly soluble (70–80%) at either pH. An increase in acidity lead to protein unfolding, an increase in random coil structure and the appearance of lower molecular weight proteins due to acidic hydrolysis. These structural changes at pH 4 increased the capacity for foam formation and foam stability, increased viscosity and led to concentration and age dependent thickening. Gels, similar in strength but with distinct microstructures and properties were obtained following heating. At pH 7, a particulate type gel with an interconnected protein network was formed, while the gel at pH 4 had a dense continuous protein matrix. The gels differed in their susceptibility to chemical disruption, suggesting different underlying molecular interactions. The ability to alter protein structure and properties as a function of pH and heating could be used to broaden the application of almond proteins and develop a variety of food products, such as protein supplements and vegan alternatives to traditional products.
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ItemNo Preview AvailableNutrient enrichment of dairy curd by incorporation of whole and ruptured microalgal cells (Nannochloropsis salina)(Elsevier, 2022-12-01)This work investigated incorporation of Nannochloropsis salina into renneted dairy gels and curd. Whole and ruptured microalgal cells did not impair κ-casein macropeptide cleavage by the rennet enzyme. However, insoluble components of ruptured cells impeded gelation, presumably by hindering interactions between renneted casein micelles. Confocal imaging showed that whole cells were retained and homogenously distributed within the protein network of the gels and cooked curd, whereas ruptured algae formed large aggregates that altered the protein matrix. Eicosapentaenoic acid (EPA) in the whole microalgal cells was incorporated within the curds, with considerably less EPA retained for ruptured cells. Soluble algal debris did not impair gelation, however EPA wasn't retained in the curd. The study demonstrates that nutrient enrichment of renneted dairy products is possible by incorporating whole microalgal cells to displace milk fat with protein and the beneficial long-chain omega-3 fatty acid EPA. Future research into the optimisation of product organoleptic properties is required.
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ItemNo Preview AvailableBeta casein proteins-A comparison between caprine and bovine milk(ELSEVIER SCIENCE LONDON, 2022-03)
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ItemPlant and Dairy-Based Yogurts: A Comparison of Consumer Sensory Acceptability Linked to Textural Analysis(MDPI, 2022-02)Yogurt, readily available in plant and dairy-based formulations, is widely consumed and linked with health benefits. This research is aimed to understand the sensory and textural spectrum of commercially available dairy and plant-based yogurts. In a preliminary study, qualitative focus group discussions (4 groups; n = 32) were used to determine perceptions of 28 dairy and plant-based yogurts, identifying positive consumer perceptions of plant-based yogurts. A smaller subset of five spoonable and one drinkable yogurts-(Reference, Soy, Coconut, Cookies, Berry, and Drinkable) was subsequently selected for rheological and structural measurements, showing wide variations in the microstructure and rheology of selected yogurt samples. A quantitative blind sensory tasting (n = 117) showed varying yogurt acceptability, with Berry being the least-liked and Cookies being the most-liked yogurt, in terms of overall liking. The multi-factor analysis confirmed that compositional and textural elements, including protein content, gel firmness, and consistency coefficient, displayed a positive relationship with overall liking. In contrast, fat, sugar, and calories were negatively correlated to the overall liking. This research showed that texture and other compositional factors are significant determinants of the consumer acceptability of yogurt products and are essential properties to consider in product development.
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ItemDifferences in Hedonic Responses, Facial Expressions and Self-Reported Emotions of Consumers Using Commercial Yogurts: A Cross-Cultural Study(MDPI, 2021-06)Hedonic scale testing is a well-accepted methodology for assessing consumer perceptions but is compromised by variation in voluntary responses between cultures. Check-all-that-apply (CATA) methods using emotion terms or emojis and facial expression recognition (FER) are emerging as more powerful tools for consumer sensory testing as they may offer improved assessment of voluntary and involuntary responses, respectively. Therefore, this experiment compared traditional hedonic scale responses for overall liking to (1) CATA emotions, (2) CATA emojis and (3) FER. The experiment measured voluntary and involuntary responses from 62 participants of Asian (53%) versus Western (47%) origin, who consumed six divergent yogurt formulations (Greek, drinkable, soy, coconut, berry, cookies). The hedonic scales could discriminate between yogurt formulations but could not distinguish between responses across the cultural groups. Aversive responses to formulations were the easiest to characterize for all methods; the hedonic scale was the only method that could not characterize differences in cultural preferences, with CATA emojis displaying the highest level of discrimination. In conclusion, CATA methods, particularly the use of emojis, showed improved characterization of cross-cultural preferences of yogurt formulations compared to hedonic scales and FER.