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Frankfurt (Main), Univ., Diss., 2009 / Erscheinungsjahr an der Hauptitelstelle: 2008

Thesis (doctoral)--University of Konstanz, 2004. / Includes bibliographical references (p. 157-173).

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Inhibition of blueberry PPO activity by sodium benzoate, potassium sorbate and potassium metabisulfite and their influence on degradation of individual anthocyanins in an extract was studied. Maceration of blueberries was carried out at 55ºC for 1h with the addition of 0.1% sodium benzoate or with blanching pretreatment at 90ºC for 1min. After maceration pretreatments the extracted juice was processed with traditional hot fill pasteurization, high hydrostatic pressure (HHP) and pulsed electric field (PEF). Sodium benzoate and potassium metabisulfite were very effective PPO inhibitors in concentrations of 0.1% and 10ppm, respectively. Potassium sorbate was the weakest inhibitor, with 50% PPO remaining. Degradation of anthocyanins by PPO was dependent on their structure. Tri-phenolic anthocyanins experienced the most degradation, followed by diphenolic and monophenolic compounds, respectively. Sodium benzoate was the most effective at preventing anthocyanin degradation; potassium metabisulfite did not have any protective effect, while potassium sorbate increased anthocyanin degradation Blanching of blueberries inactivated native PPO, but also increased the degradation of anthocyanins, especially malvidin glycosides. Addition of 0.1% sodium benzoate decreased PPO activity when compared to frozen blueberries but not in respect to control maceration. Only 12% of anthocyanins and 33-41% of phenolics were extracted into juice from the frozen fruit. Hot fill pasteurization, high hydrostatic pressure and pulsed electric field did not significantly influence anthocyanins, phenolics and antioxidant activity in blueberry juice.

Published Article / Alicyclobacillus acidoterrestris is a non-pathogenic, spore-forming bacterium that can survive the commercial pasteurisation processes commonly used during fruit juice production. Surviving bacterial endospores germinate, grow and cause spoilage of high acid food products. Fruit juices can be treated using ultraviolet light (UV-C) with a wavelength of 254 nm, which has a germicidal effect against micro-organisms. In this study, A. acidoterrestris was inoculated into water, used wash water from a fruit processing plant and grape juice concentrate. Ultraviolet dosage levels (J L-1) of 0, 61, 122, 183, 244, 305 and 367 J L-1 were applied using a novel UV-C turbulent flow system. The UV treatment method was shown to reliably achieve in excess of a 4 log10 reduction (99.99%) per 0.5 kJ L-1 of UV-C dosage in all the liquids inoculated with A. acidoterrestris. The applied novel UV technology could serve as an alternative to thermal treatments of fruit juices for the inactivation of Alicyclobacillus spores as well as in the treatment of contaminated wash water used in fruit processing.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Master of Science / Food Science Institute / Daniel Y.C. Fung / The process of canning or “commercial sterilization” has been studied for more than two centuries. The first to develop canning as a defense against spoilage was Nicholas Appert also known as the “father of canning.” Appert invented a method of preservation by enclosing food in hermetically sealed containers and then heating containers to boiling temperatures for a specific period of time. The canning preservation method has changed over the years, and continues to change for the better. Technology for retorts, or processing vessels, has grown from the traditional steam heating medium to also include water and steam/water spray heating mediums. The once static vessels, now utilize rotation and shaking motions to decrease process time and in turn increase product quality. The product packaging has also evolved to include not only rigid metal containers, but semi-rigid and flexible plastic containers. The variety of packaging adds greater flexibility to the type of food products that can be produced in a shelf stable manner. Canning or “commercial sterilization” is still used today by the food industry as a method of providing safe food with extended shelf life. Today’s goal of commercial sterilization is to continue to produce safe food products that are high in quality and profitable to produce. A variety of processing equipment is available to accomplish those goals, ranging from a basic steam retort to the newest technology on the market known as Shaka. This new retort technology uses reciprocal agitation to shorten processing times and increase the quality of the final products. Studies have shown that the Shaka process reduces processing times better than 20-fold compared to a still process and better than 10-fold compared to a rotary process. As the field of thermal processing continues to evolve, the challenge will be to consistently produce safe, commercially sterile food that exceeds current quality expectations in a shorter process time while using less energy. Shaka, and other new technologies, will help the food industry meet these challenges and expectations by expanding the current capabilities of thermal processing to meet consumer demands.

Peanut allergy typically results from sensitisation to one or more integral seed storage proteins; Ara h 1, 3 or 2/6. Reactions can be triggered by as little as 3 mg protein in 10% of allergic individuals and are often severe, inducing anaphylaxis which can be fatal. Accidental exposure through unintended presence can therefore be hazardous and foods must be labelled appropriately. Thermal processing is one of the main factors affecting protein properties in food systems, including the formation of Maillard reaction products. Research has suggested a link between the allergenicity of foods and cooking methods employed. A systematic study was undertaken to assess the thermal dependence of these hazard proteins, focusing on changes to solubility and chemical modifications which may alter IgE binding. Proteomic profiling was used to assess the allergenic content of peanut products and develop alternative methods for allergen analysis to support evidence-based application of precautionary allergen labelling. Runner variety peanuts were processed (boiled, fried, roasted) and their protein content determined. Proteins extracts were characterised by 1D- and 2D-polyacrylamide gel electrophoresis, including differential in-gel electrophoresis. Proteomic profiling was undertaken using label-free analysis to assess allergen composition and investigate the formation of Maillard reaction products on the most clinically relevant proteins. Peanut allergen peptide targets were then identified and used to develop label-based quantitation methods and applied to (i) investigate effects of processing on peptide targets and (ii) determine peanut in chocolate products in comparison with a commercial ELISA kit. Orthogonal studies were performed using serum samples from peanut allergic patients obtained from the Manchester Respiratory, Allergy and Thoracic Surgery (ManARTS) Biobank. Patient IgE reactivity to peanut and processed peanut products was assessed by immunoblotting, inhibition ELISA and mediator release assays. Protein solubility was reduced by thermal processing and processed protein required harsh denaturing conditions for extraction. Qualitative analysis highlighted decreased solubility of key allergens, modifications and aggregation after heating. Proteomic profiling identified and quantified different isoforms of the major peanut allergens. The protein content of processed peanuts was reduced by boiling, specifically the 2S albumins, which transferred into the cooking water. The performance of peptides selected for targeted MRM experiments was influenced by thermal processing and the presence of cocoa phenolics. Ara h 2 peptides flanked by arginine were thermostable and may prove more reliable for quantification. Application of microfluidic separation enhanced the efficiency of target ionisation in complex matrices acquiring important sensitivity gains. Maillard modifications to clinically relevant proteins Ara h 2/6 were found within IgE binding domains in raw and processed peanuts. IgE reactivity studies confirmed reduced IgE binding capacity of extensively boiled peanut and hydrolysed protein, but this did not correlate to a reduction in mediator release in poly-sensitised patients. While effective extraction limits the efficacy of analyses, buffers used in MS analyses are more robust in analysing processed protein. Proteomic profiling provides a means of characterising and profiling of allergenic proteins including food ingredients used in clinical applications. Peptides selected for targeted analyses should be validated to assess their suitability in model foods. Cooking waters collected from extensively boiled peanuts may provide an alternative and safer immunotherapy agent for patients predominantly sensitised to Ara h 2/6.

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