Graduation date: 1991

Graduation date: 1980

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 67-69).

Thesis (M.S.)--Oregon State University, 1986. / Typescript (photocopy). Includes bibliographical references (leaves 94-98). Also available on the World Wide Web.

M.Tech.

Bacteriocins (BCNs) are ribosomally synthesized polypeptides or proteins with antimicrobial activity, produced by different groups of bacteria. Many lactic acid bacteria (LAB) produce BCNs with broad spectra of inhibition. The antimicrobial activity of BCNs against spoilage organisms (SPOs) has raised considerable interest in their application in juice preservation. The objectives of the study were to: (i) isolate, identify and screen BCN producing bacteria for antimicrobial activity against spoilage bacteria and fungi, (ii) optimize production of BCN from selected producers and (iii) investigate the industrial application of the BCN as a preservative in fruit juice. Eleven LAB strains of BCN producers were screened for antimicrobial activity. BCNs from Lactobacillus plantarum and Pediococcus pentosaceus 34 were the most effective against juice spoilage bacteria and fungi. The effect of medium components on bacteriocin production in L. plantarum and P. pentosaceus 34 was also determined. Clementine:Valencia (1:1) juice was used for the first time as the growth medium for L. plantarum and P. pentosaceus 34. The BCN from L. plantarum showed the highest activity and was, therefore, chosen for juice fermentation studies. The identification of L. plantarum was confirmed by biochemical tests, polymerase chain reaction (PCR) and sequencing of the recA gene. The highest BCN activity was observed for L. plantarum grown in De Man-Rogosa-Sharpe (MRS) and a combination of all supplements (i.e. peptone, MnSO4.H2O, Tween 80, glucose and whey), followed by MRS and Tween 80, peptone, MnSO4.H2O and MRS alone. MRS was a better medium for BCN production than juice [Clementine:Valencia (1:1)]. Size exclusion chromatography (SEC) was used to isolate the active L. plantarum BCN fraction which corresponded to an approximate molecular weight of 3.2 kDa and was proteinaceous in nature. Plantaricin structural genes (plnEF, plnJ, plnK, plnN) were detected in the L. plantarum strain by PCR and sequenced, and were chromosomally encoded as no plasmids could be detected. This implies that the BCN from L. plantarum is most likely a type of class IIa plantaricin which is responsible for the broad inhibitory activity observed. For the industrial application studies, L. plantarum BCN-containing cell free supernatant (BCNsup) added to “Ready to Drink” (RTD) Clementine:Valencia (1:1) juice at concentrations of 3 600 - 500 000 ppm decreased growth of SPOs, Lactobacillus acidophilus and Streptococcus thermophilus. At 250 000 ppm, the L. plantarum BCNsup achieved 5.3 and 6.8 log reductions of the L. acidophilus, after 24 and 48 h, respectively, which is larger than the USFDA (2001) requirement of a 5 log reduction in SPO activity, for preservation of fruit juices. However, there was a decrease in the activity when the BCNsup was applied to industrial (Valor) RTD juice (mango-orange) at decreasing concentrations of 100 000, 50 000 and 25 000 ppm. Organoleptic tests showed that the BCN did not alter flavor or taste of the juice and did not cause toxicity or allergic reactions. A food safety risk assessment was conducted in order to determine the Critical Control Point(s) [CCP(s)] at which the BCN could be applied to control identified microbiological hazards, and a Hazard Analysis and Critical Control Point (HACCP) plan was developed. This is the first report on the optimisation of L. plantarum BCN production in juice [Clementine:Valencia (1:1)], followed by inoculation into RTD juice (mango-orange), including a HACCP plan for the application of the BCN as a preservative in juice.

Response Surface Methodology (RSM) was used to study the effect of two variables, sugar level (12-16 °Brix) and acid level (0.3-0.7 % T.A.) on sensory qualities and desirability of blackberry juice drinks. Three blackberry juice levels (10%, 15%, and 20%) were used to study the influence of juice flavor on sensory qualities and desirability of the juice drinks. A trained panel evaluated three attributes, blackberry flavor, sweetness, and sourness intensities, of the juice drinks. The consumer panel gave desirability and three attributes just-right ratings. A Balanced Complete Block Design was used. Blackberry flavor intensity was enhanced by sugar level. Blackberry flavor intensity was enhanced by acid level to a point about 0.5% T.A., and then decreased. Blackberry flavor intensity was not related to °Brix:acid ratio and was only related to the sweetness:sourness ratio at the 20% juice level. Sweetness and sourness intensities increased with increasing sugar and acid levels. There was a suppression effect of sugar and acid on each other in the juice drink. The relationships of sweetness, sourness, and sweetness:sourness ratios to °Brix:acid ratios were all linear. Desirability rating was related to °Brix:acid and sweetness:sourness ratios for the 10% and 20% juice levels, for 15% juice level no association was found. The formula which received the closest to "just right" ratings and highest overall desirability rating had in a °Brix of 15.4 and a % titratable acidity of 0.64, resulting in a °Brix:acid ratio of 24 and a corresponding sweetness:sourness ratio of slightly less than 1.0. In general, the 15% juice level was the best because of its sugar and acid tolerance and high desirability. / Graduation date: 1989

It has long been recognized that fermented food products possess a characteristic but pleasant flavor. The use of such foods, however, has been limited by the presence of ethanol. Thus the objective of this research was to investigate the possibility of producing non-alcoholic fermented juice concentrates. Three varieties of juices, Concord grape, apple, and blackberry, were ameliorated as needed and fermented to five to seven percent alcohol by volume. The fermented flavor was extracted with ethyl chloride and concentrated by distillation. These extracts were analyzed by gas chromatography using two different column temperatures. Low column temperature was 100°C while high column temperature was 170°C. Four peaks were found to contribute from 93 to 97 percent of the flavor compounds chromatographically separated from the three juices at low temperature. By use of the enrichment technique, these peaks appeared to be propyl alcohol, isobutyl alcohol, butyl alcohol, and a mixture of isoamyl and active amyl alcohol. At high temperature separation, four peaks were observed to comprise 56 to 64 percent of the flavor components fractionated. These four peaks appeared to be a mixture of acetic acid and ethyl octanoate, caproic acid, phenethyl alcohol and caprylic acid. Other components were tentatively identified to be acetone, ethyl acetate, ethanol, n-amyl alcohol, ethyl hexanoate, n-hexanol, propionic acid, 2, 3-butylene glycole, butyric acid, isovaleric acid, diethyl succinate, 4-butyrolactone, valeric acid and capric acid. Freeze drying and a combined method of distillation and freeze centrifugation were the two methods employed to remove ethanol and water from the fermented juices. A fivefold concentration of the original juices was obtained. From 91 to 95 percent of the alcohol and 80 percent of the water were removed from the juices by freeze drying while the combined technique removed only 79 percent of the ethanol and 80 percent of the water. Total acids, color and total soluble solids were not affected by the freeze drying procedure whereas the combined technique for removal of the alcohol resulted in some loss of these constituents. The fermented dealcoholized juices were analyzed by gas chromatography using only high temperature columns. These data indicate that dealcoholization resulted in a decrease in the peak heights of the first ten peaks to be separated. The remainder of the peaks generally showed an increase although a few exceptions were noted. The dealcoholized fermented juice concentrates were reconstituted and evaluated by a flavor panel. The panel data indicated that the rank order of preference for the three juices was blackberry, apple and Concord grape. The flavor panel also preferred the juices served at the higher levels of sweetness. The total average panel score for these three juices was observed to be about a neutral rating of "neither like nor dislike". / Graduation date: 1966

No description available.

Graduation date: 1953