1,720,995 research outputs found
Mechanical and charge transport properties of alkanethiol self-assembled monolayers on a Au(111) surface: The role of molecular tilt
No full textThe relationship between charge transport and mechanical properties of alkanethiol self-assembled monolayers (SAMs) on Au(111) films has been investigated using an atomic force microscope with a conductive tip. Molecular tilts induced by the pressure applied by the tip cause stepwise increases in film conductivity. A decay constant beta = 0.57 +/- 0.03 angstrom(-1) was found for the current passing through the film as a function of tip-substrate separation due to this molecular tilt. This is significantly smaller than the value of similar to 1 angstrom(-1) found when the,separation is varied by changing the length of the alkanethiol molecules. Calculations indicate that, for isolated dithiol molecules S-bonded to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of S-Au bonding on SAM conductance is discussed
Microencapsulation of Perilla Seed Oils with Different Wall Materials
No full textFull text is available to authenticated members of The University of Auckland only.Perilla fructescens, referred to as perilla, is an annual member of the Lamiaceae family. It is an edible and medicinal plant and widely cultivated in hills and mountains of East Asia. Perilla leaves are applied in herbal medicine for symptoms of asthma and cough and its seeds support healthy immune function, prevent coronary heart disease and decrease blood clotting due to its high content of n-3 linolenic acid. Perilla seeds are a source of perilla oil containing a large amount of unsaturated fatty acid which is sensitive to light and easy to oxidise causing a nutritional loss. Microencapsulation technology is one of methods used to improve the shelf life of valuable oils by enclosing the oil droplets with protective wall materials. Through spray drying, the oxidative-sensitive oil droplet could be transformed into a solid form through rapid evaporation of solvent in the droplets. This study aimed to investigate spray drying microencapsulation of perilla seed oil (both red seed and white varieties) using a combination of wall materials including whey protein isolate (WPI), gum Arabic (GA), maltodextrin (MD) and starch sodium octenyl succinates (OSA starch). The effects of core-to-wall ratio (1:3 and 1:4), solid content (15% and 30%), wall materials and complex coacervation were conducted to see its effect on emulsions and spray-dried microcapsules. Optimisation of emulsion preparation was studied as the first step, followed by characterization of emulsions and spray-dried microcapsules. For emulsions, characteristics were investigated include average droplet size, PDI and zeta-potential. The microencapsule properties included moisture content, water activity, density, oil recovery, encapsulation efficiency (EE), morphology, reconstituted properties and oil were also studies. The oxidative stability of emulsion and spray-dried microcapsules were studied using a accelerated storage trial at 55oC without light by evaluating peroxide value (PV), p-Ansidine (AV) and DPPH antioxidant capacity. The results showed that both emulsions and microcapsules produced at core-to-wall ratio of 1:4 using OSA starch as wall material lead to the minmum changes of PV, AV and DPPH antioxidant capacity. Microencapsules in the present research produced with different wall materials, ratios of core-to-wall and solid contents had a lower water acivity (0.2 < Aw < 0.3), good moisture content (4% - 9%) for long-term storage, high EE (87% - 98%) and good reconstituted ability of spary-dried microcapsules. The microcapsules produced by feed emulsions with core-to-wall ratio of 1:4, 30% solid content using OSA starch as wall materials had the most effective formulation during accelerated storage test. And also, the oxidation stability of both emulsions and microcapsules could be improved via complex coacervation. In conclusion, the present study provided insight to microencapsulation of perilla seed oil using the spray drying method, which improved oxidative stability and inhibited oxidative deterioration
Development of a Customisable Food Fraud Vulnerability Ranking Tool
No full textTo make the best use of limited resources, regulatory authorities and food companies must prioritise risk management actions towards risk-based approaches. They should also focus on risks with the greatest public health impact. Food safety crises can lead to substantial costs to corporations, countries, consumers, and even for an entire food segment ‘from farm to fork’. In this scenario, food fraud must be effectively prevented and mitigated after a suitable vulnerability assessment based on the most relevant knowledge available. The purpose of this study was to develop a robust method for evaluating public health and economic impact of food fraud, in addition to the assessment of vulnerability factors proposed by expert panels. In other words, a spreadsheet wherein a regulatory agency or a food corporation, could evaluate these three components together by customising the relative weights, and designing and adjusting criteria to make more informed decisions, thus prioritising the allocation of resources. The criteria were mainly data-driven, based on nearly 1,000 food fraud incident records from around the globe. All relevant information recorded in the United States Pharmacopeia (USP) Food Fraud Database has been analyzed to provide invaluable prevention and mitigation insights. The tool is divided into three main modules. The red module refers to the public health assessment, the blue assesses the vulnerability of the ingredients, and the green and last module evaluates the economic impact. The methodology chosen is based on two main benchmarks: a US-FDA risk-ranking tool for microbiological hazards in fresh produce and a New Zealand document from the Ministry for Primary Industries used to update entire food legislation towards a risk-based approach. Furthermore, the USP Mitigation Guidance developed by a food fraud expert panel was essential in determing some public health criteria, supplemented by World Health Organization-risk assessment principles. Finally, this tool has been tested to compare food ingredients regarding their vulnerability and impact on decision-making processes of risk managers by assessing public health factors and the food fraud history. Resources can be directed towards higher risks and weaker points to prevent and mitigate negative public health exposure and the financial impact. Keywords: food fraud, risk-based approach, risk-ranking tool, vulnerability assessment, and USP Food Fraud Database
The volatile composition and aroma profile of ‘Unique’, ‘Triumph’ and ‘Anatoki’ feijoa fruits (Acca sellowiana) during ripening
No full textFull Text is available to authenticated members of The University of Auckland only.Feijoa (Acca sellowiana) is a climacteric fruit which is widely planted in the Mediterranean region, Tunisia, USA, Australia and New Zealand. Although the functional and biochemical properties of feijoa fruits have been well-recognised, the volatile composition and aroma profile are less studied. This study focused on the analysis of the free and bound volatiles, as well as identification of aroma active compounds of feijoa fruits. Factors include fruit ripening stages and cultivar difference could influence the synthesise of fruit volatiles. Therefore, feijoa fruits from different cultivars and ripening stages were selected to give a deeper insight of aroma profile of feijoa fruits. Feijoa fruits from the ‘Unique’, ‘Triumph’ and ‘Anatoki’ cultivar were collected at four ripening stages (four weeks before ripening, two weeks before ripening, ripe and overripe). Their volatile was analysed by headspace solid phase microextraction (HS-SPME), gas chromatography mass spectrometry (GC-MS) and olfactory tests (GCO). A total of 164 free volatiles with 60 terpenes, 52 esters, 20 alcohols, 9 ketones, 6 aldehydes, 2 hydrocarbons and 15 unknowns were identified. Terpene was the dominant group in the unripe fruits, whereas ester was the dominant class in the ripe and overripe fruits. During ripening, the concentration of free terpenes, alcohols and ketones decreased while that of ester largely increased. A total of 26 aroma active compounds were identified. At unripe stages, terpene dominated the free aroma and released a ‘herbal and grassy’ odour. At ripe and overripe stages, esters dominated the free aroma profile and gave a ‘fruity, sweet and floral’ aroma. The key aroma active compounds were found to be ‘sweet, floral and fruity’ ethyl butanoate and ‘fruity, feijoa-like’ methyl benzoate and ethyl benzoate, ‘floral and fresh’ linalool, ‘fruity and green’ α- cubebene and ‘grass and woody’ caryophyllene. A total of 84 bound volatiles with 28 terpenes, 19 alcohols, 9 aldehydes, 8 ketones, 3 esters, 1 hydrocarbon and 16 unknowns were identified and 52 of them co-existed as free and bound volatiles. Bound alcohol, terpene and ketone were the main groups in the 4 weeks before ripening fruits and aldehyde was the dominant class in the 2 weeks before ripening fruits. In the ripe and overripe fruits, the major groups varied among the three cultivars. Comparable with the free terpene and ester, the bound terpene decreased while the bound ester increased. Both the number and concentration of bound volatiles were much lower than those of the free volatiles. The importance of bound volatiles to its whole volatile composition in feijoa fruits could be limited due to their lower number and insignificant concentrations. To sum up, the present thesis is the first study that focused on the analysis of free and bound volatile compounds in the whole feijoa fruit at different ripening levels. The study of feijoa volatile composition and aroma profile of feijoa fruits at different ripening stages could bring substantial insight into this fruit and give deeper understanding into fruit ripening and fruit aroma
Encapsulation of fish oil and astaxanthin using whey protein isolate and polysaccharide wall matrix
No full textFull text is available to authenticated members of The University of Auckland only.Fish oil and astaxanthin are two functional ingredients with health benefits to humans, however both are susceptible to oxidation during processing. This study aimed to investigate the microencapsulation of fish oil and astaxanthin by spray drying them with whey protein isolate (WPI) and either maltodextrin (MD) or soluble corn fiber (SCF) to act as wall materials. The emulsions consisted of different wall/core ratios (4:1 and 2:1) and protein/polysaccharide ratios (2:1, 1:1, and 1:2) were prepared using a high-speed homogenizer first and then a high-pressure homogenizer. The average droplet size, particle size distribution and zeta-potential were evaluated, as well as the changes in antioxidant capacity and the oxidation extent of the core material, during 15-day storage trials. The emulsions that gave the best stability were then spray dried into microcapsules at inlet temperatures of both 160 °C and 180 °C. The characteristics of the microcapsules, including water activity, surface oil, encapsulation efficiency and reconstitution properties, were investigated. In addition, the storage stability of each microcapsule was compared with that of the original emulsion. Finally, an in vitro digestion assay was conducted to study the digestibility of the microcapsules. All the formulated emulsions showed narrow droplet size and particle size distribution, with the emulsions with a wall/core ratio of 4:1 and a protein/polysaccharide ratio of 2:1 having the best stability. The results indicated that the blending of astaxanthin and fish oil could effectively inhibit the oil phase oxidation, resulting in better stability. The inlet temperature of 160 °C showed better microcapsule physical characteristics, including good water activity, lower surface oil content, and higher encapsulation efficiency. Scanning electron microscopy revealed that the microcapsules had surface dents but no cracks, which could support core preservation capacity. The microcapsules were also found to have higher stability than that of the original emulsions. The in vitro digestion assay confirmed the bioaccessibility of EPA, DHA, and astaxanthin at the intestinal phase. It also illustrated that fish oil and astaxanthin spray dried with a combination of WPI and MD resulted in better digestibility than those spray-dried with a combination of WPI and SCF. Overall, this research demonstrates that spray drying for microencapsulation is a potential means of enhancing the stability of fish oil and astaxanthin, and that the co-encapsulation of astaxanthin with fish oil could further enhance the stability of fish oil in microcapsules
Co-encapsulation of Vitamin E and Coenzyme Q10 using Octenyl Succinic Anhydride Modified Starch
No full textFull text is available to authenticated members of The University of Auckland only.Vitamin E (VE) and Coenzyme Q10 (CoQ10) are two groups of lipophilic antioxidants that are known to possess synergistic effects when working together as co-antioxidants against lipid peroxidation. This study investigated the co-encapsulation of VE and CoQ10 by spray drying, using octenyl succinic anhydridemodified starch (HICAP100) as wall material. VE and CoQ10-containing emulsions (10, 20 and 30% w/w solid content; 2/1 and 4/1 HICAP100/oil ratios) were prepared by high-pressure homogenizer processing at 80 MPa for 3 homogenization passes. Characterisation was performed to evaluate the droplet size, rheological properties and stability of emulsion composed of different formulations. Selected emulsions (10 and 30% w/w solid content; 2/1 and 4/1 HICAP100/oil ratio) were investigated for their droplet drying and dissolution behaviour using the single droplet drying technology. The same emulsions were then transformed into powders by spray drying at 160 and 190 °C inlet temperatures. Powder properties including the microcapsule morphology, moisture content, encapsulation efficiency (EE) and density were determined. Stability of microcapsules were assessed by evaluating the change in colour, retention of VE and CoQ10 and DPPH radical scavenging activities throughout 21 days of storage at both 25 and 45 °C. All emulsions produced using HICAP100 as an emulsifier had droplet size below 0.2 m with narrow size distribution. Viscosity varied across emulsions with different solid content, but this exhibited little effect during the spray drying process. Scanning electron microscopy (SEM) showed shriveled, irregular and wrinkled surface of spray-dried microcapsules caused by particle shrinkage during the drying process. Microcapsules produced from 10% w/w solid content emulsions were observed with greater shrinkage compared to those produced from 30% w/w solid content emulsions, which was in agreement with results obtained from single droplet drying. High EE (> 96%) and recovery of VE (> 85%) and CoQ10 (> 75%) were obtained for all spray-dried microcapsules, indicating HICAP100 was an effective wall material for the protection of core encapsulated materials during the spray drying process. When stored at 25 °C, microcapsules were observed with reasonably good stability, with minimal loss of their initial powder colour, core bioactive components, and antioxidant properties after 21 days of storage. When stored at 45 °C, microcapsules spray-dried at 190 °C, which had significantly lower initial moisture content, showed better stability than those spray-dried at 160 °C. Also at 45 °C storage temperature, microcapsules with 4/1 wall/core ratio resulted in higher retention of the encapsulated bioactive components than those with 2/1 wall/core ratio. The results from the storage test combine to suggest the importance of controlling the initial moisture content and also the wall/core ratio to promote stability of microcapsules during long-term storage. In summary, the present study provided insight to co-encapsulation of VE and CoQ10 using the spray drying method, which can be used as a way to enhance their stability and application in food systems
Microencapsulation of Astaxanthin with Different Blends of Protein and Soluble Corn Fibre Using Spray Drying
No full textFull text is available to authenticated members of The University of Auckland only.Astaxanthin is an active antioxidant and has beneficial effect on human health. However, its hydrophobic nature and susceptibility to light, heat and oxygen limit its application in most food systems. This study aimed to encapsulate astaxanthin using milk proteins and carbohydrate, in order to improve its stability and application in food systems. Whey protein isolate (WPI) and sodium caseinate (SC) are well known encapsulants and possess antioxidant properties. Soluble corn fibre 70 (SCF70) with DE 20 is believed to exhibit antioxidant activity and to improve encapsulating capacity of protein-based wall systems. They were therefore selected as the wall materials for encapsulation of astaxanthin. The wall solution was prepared from dissolving the emulsifier and carbohydrate containing a total of 20-24 wt% solids in water. The astaxanthin emulsions were prepared by two-stage homogeniser at 80 + 800 bars after passing through the homogeniser 4 times. The emulsion were then converted into powders with 0.33 wt% astaxanthin by spray drying at 160°C inlet air temperature and 70°C outlet air temperature. The properties of the emulsions were evaluated including droplet size, size distribution, zeta potential, and viscosity. The powder produced from spray drying were characterised by chemical and physical tests including water activity, microencapsulation efficiency, surface properties and oxidative stability. The interaction between wall materials was studied using Fourier Transform Infrared Spectroscopy (FTIR) while the bioaccessibility was investigated in an in vitro digestion study. Results show that droplet size of the astaxanthin emulsions was below 200 nm and size distribution appeared to be narrowly distributed. Therefore, particle size would have little effect on the physicochemical properties of spray dried powders. The low viscosity of the parent emulsions probably exhibited little effect on the spray drying process. It was found that the reconstituted emulsion and parent emulsion both had droplet size below 200 nm. This indicates that the astaxanthin emulsions could be stable during spray drying. Scanning electron microscopy reveals that formation of surface dents on some samples caused by particle shrinkage during early drying process. Particle with WPI based wall systems had smoother outer surface than those formulated with SC based wall matrices, suggesting that WPI could be a suitable encapsulating agent in combination with soluble corn fibre 70. Microencapsulation efficiency of the microencapsulated astaxanthin was above 88%, indicating the wall matrices were effective in preventing penetration of the organic solvent into the microcapsule. Storage test was conducted at 45°C and 33% relative humidity, under air and nitrogen environment. The oxidative stability of the astaxanthin microcapsules was determined by measuring peroxide value and p-anisidine value. Results show that surface oil might not be related to the oxidative stability of the microcapsules and other factors might adversely affect the oxidative stability. Changes in the physical state of the amorphous powders due to the difference in water activity between the powders and storage environment might influence the oxidative stability and the astaxanthin content in the microcapsules. Results indicate that wall composition may have little effect on the oxidative stability of the microencapsulated astaxanthin. Astaxanthin content in microcapsules with high oil content decreased slightly faster than in those containing less oil content. Oxidative stability of the microcapsules could be related to the antioxidant activity of raw materials. The FTIR results indicated the possibility of Maillard reaction products formation, which may also influence the oxidative stability of the microcapsules. The in vitro digestion results suggested that the digestivity of the WPI based wall systems might be better than that of the SC based wall systems, as the bioaccessibility of the microcapsule were higher. The presence of dietary fibre (i.e., SCF70) and wall thickness might affect the in vitro digestivity of the microcapsules. Overall, the best formulation showing the best bioaccessibility (71.67%) is the WPI/SCF 70 ratio of 1/0.5 and the wall/core ratio of 2. In summary, this research has shown that microencapsulation of astaxanthin by spray drying technique is capable of producing a more stable microcapsule that has potential application in food system
Co-encapsulation of vitamin E and Coenzyme Q10 with different blends of protein and carbohydrate through microfluidic jet spray dryer
No full textFull text is available to authenticated members of The University of Auckland only.Vitamin E and coenzyme Q10 (CoQ10) exhibit effective antioxidant activity which can be enhanced through their synergistic interaction. Lacking these two antioxidants may lead to serious disease in human. However, both antioxidants are sensitive to environmental factors including oxygen, light and heat. Also, they are highly lipophilic that largely limits their applicability in food. Therefore, microencapsulation of these two components through spray drying may enhance their stability and application in food systems. However, conventional spray dryer produces polydispersed microcapsules which may hinder the efficient handling of powder as well as allowing droplets to experience different evaporation process during the constant drying condition. Hence, this study aimed to co-encapsulate vitamin E with CoQ10 using milk proteins and carbohydrates through microfluidic jet spray dryer (MFJSD) to determine the synergistic antioxidant activity of vitamin E and CoQ10 in microcapsules as well as enhancing their stability and applicability in food system. Whey protein isolate (WPI) is widely used emulsifier to encapsulate food ingredients that also exhibit antioxidant activity. Carbohydrates are also commonly used as stabilisers and blending proteins with carbohydrate is known to improve encapsulation efficiency and stability of microcapsules. Therefore, maltodextrin (National M3) and soluble corn fibre (PromitorTM soluble corn fibre 70) were employed as stabilisers. By blending with WPI, these carbohydrates were used to encapsulate vitamin E and CoQ10. Wall materials were dispersed in water either blended or alone to prepare the wall solution with 30% solids. The emulsions containing vitamin E and CoQ10 were produced by ultraturrax homogeniser at 13,500 rpm which was further homogenised by nano-homogenize machine at 800 ± 50 bars for 6 passes. The conversion of emulsion into powders were achieved by spray drying at 190ºC inlet and 90ºC outlet air temperature using disturbance frequency between 6,000 to 8,000 kHz. The emulsion characteristics studied were emulsion droplet size, size distribution, viscosity and its stability. The properties of powder were determined including moisture content, density, flowability, wettability, morphology, core material retention. The storage stability of microcapsulesat room temperature was carried out by evaluating change in the colour, microencapsulation efficiency and oxidative stability of microcapsules. Microcapsule digestibility was assessed by using in vitro digestion study. Results describe that the droplet size of all emulsions was below 200 nm with narrow size distribution. The viscosity of the emulsions was low and visual observation with emulsion droplet measurement indicated the sufficient stability of emulsions during spray drying. Microcapsules prepared by WPI had the highest mean moisture content where the mean density was the greatest in microcapsules prepared by WPI and SCF and the lowest powder flowability was indicated from microcapsules prepared by WPI and M3. The wetting time of microcapsule was the longest in microcapsules prepared by WPI compare to the blend WPI with carbohydrates. Scanning electron microscopy showed the apparent surface cracks on microcapsule prepared by WPI and surface dents on microcapsule prepared by WPI and WPI with M3. Uniformity in the size of microcapsules was apparent in microcapsules produced by WPI and WPI with SCF. The retention of core materials in all microcapsule was above 90%, indicating effective retention of core materials in microcapsules. Storage test performed at room temperature (=25°C) determined that the initial microencapsulation efficiency of all microcapsules was 90% that slightly reduced over time. This proves the effectiveness of wall system against organic solvent penetration through the wall matrices. Colour parameters measured during the storage test show that the original colour of the wall materials and non-enzymatic browning occurred between wall materials can influence the overall colour of microcapsules. Oxidative stability results conducted for storage trial showed that co-encapsulating vitamin E with CoQ10 improved the oxidative stability of microcapsules regardless of wall materials used. However, the best synergistic antioxidant activity between vitamin E and CoQ10 was observed from microcapsules prepared byWPI with M3 indicated by the lowest IC50 value. Hence, blending WPI with M3 might give the best synergistic activity when co-encapsulating vitamin E with CoQ10 together. The in vitro oral and gastric digestion phase results show that microcapsules prepared by WPI or WPI with M3 would provide better protection of core materials than that microcapsules prepared by WPI with SCF during digestion. This is because microcapsules prepared by WPI with SCF turned into watery state immediately after the contact with water and thus core contents would be destroyed during gastric phase of digestion before reaching intestinal phase. In summary, this study has illustrated that co-encapsulating of vitamin E with CoQ10 by using MFJSD is suitable to produce microcapsules showing synergistic activity between core materials with good stability which potentially be able to be applied in food system
The Development of a Healthy Extruded Rice Product
No full textFull text is available to authenticated members of The University of Auckland only.Rice is a high carbohydrate food which is the main energy source in Asian diet for many years. It has been identified as a high glycemic index food that can increase blood sugar level causing metabolic diseases including Type 2 diabetes. In this project, yam flour, which contains higher resistant starch content than rice flour, and konjac flour, which is known as a good source of water soluble fibre were used as rice starch substitute to produce an alternative healthy rice product. Soy protein was also added to increase the protein content of the product. The ingredients used in this product formulation including yam flour was sourced from Enshi City, China where is called the “World Capital Selenium” In addition, the rice flour also contains higher selenium because it is sourced from Yichang City near to Enshi City. The rice products were developed using a twin screw extruder and the process was optimised using Response Surface Methodology applying Central Composite Design (CCD). Three factors were chosen for optimisation: percentage of yam flour (20-60%), moisture content of feed material (25-35%), and extrusion temperature (100-120oC). Also, effect of sorghum flour and extrusion screw speed was studied to improve the textural quality of the extruded products. From the results of CCD experiments, yam flour and feed moisture content were found to have positive effect on the firmness and colour properties of the products. The feed moisture content also had a direct effect on the bulk density and water absorption index of the products. On the other hand, the extrusion temperature also had a direct influence on the breaking strength of the product. Moreover, adding sorghum flour and lowering the extrusion screw speed decreased stickiness of the cooked products. Based on the physical properties, the ingredient selected to produce the extruded product with improved textural properties was 43.21% yam flour, 10% konjac flour, 5% sorghum flour, 3% soy protein and 38.79% rice flour; and the processing conditions were 25.46% feed moisture content, 120oC extrusion temperature and 12 Hz (78 rpm). This product is shown to have higher antioxidant capacity and selenium content than the commercial jasmine rice due to the high selenium content in the raw ingredient used. The sensory profile of the extruded rice products has significant different sensory profile than the commercial jasmine rice except in grain hardness. They also have lower sensory scores for product acceptability than the commercial jasmine rice, but the score was higher than 5 which could be concluded that the extruded product was accepted by consumers
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