Refrigerated Potato Strips Production
Open Access
- Author:
- Oner, Manolya Eser
- Graduate Program:
- Agricultural and Biological Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 18, 2010
- Committee Members:
- Paul Walker, Dissertation Advisor/Co-Advisor
Paul Walker, Committee Chair/Co-Chair
Ali Demirci, Committee Member
Paul Heinz Heinemann, Committee Member
Robert Bruce Beelman, Committee Member - Keywords:
- near-aseptic
blanching
ozone
levulinic acid
in-package
shelf-life - Abstract:
- The demand for fresh-cut produce has been increasing because it is nutritious, ready-to-eat or -use, convenient with minimum preparation time and fresh-like with a shelf-life up to two weeks. Chemicals, including sulfite- and chlorine-based agents, are commonly used in the fresh-cut potato industry to prevent browning and to sanitize produce. Sulfites are allowed for fresh potatoes because cooking evaporates sulfur dioxide which is considered the offending component in sulfite-sensitivity. Nevertheless, there is a concern about these compounds which can provoke allergic reactions and produce carcinogens. Frozen potato strips, although not fresh-like, are preferred in deep-fat frying because fresh and fresh-cut potato strips become soggy, limp, greasy and too dark. In this study, alternative processing and packaging techniques were investigated to produce safe and high quality refrigerated potato strips with a shelf-life up to four weeks, to be used as an alternative to fresh-cut or frozen potato strips for French frying. The effects of processing conditions —blanching time, ascorbic acid (AA) and calcium chloride (CaCl2) concentrations and potato variety— on color and textural quality of refrigerated potato strips were investigated. The highest peak force was determined in potato fries blanched at low temperature (60°C) for 30 min and then blanched at high temperature (~98°C) for 5 min. However, there was no significant difference in peak force of potato fries blanched at low temperature for 30 or 20 min followed by high temperature blanching for 10 or 5 min. Changes in blanching time did not affect the lightness of potato fries. Increasing CaCl2 concentration caused a significant increase in peak force of potato strips. Ascorbic acid did not affect color. The highest peak force was obtained in potato fries prepared from the Russet Burbank variety. The results indicate that blanching the Russet Burbank variety of potato strips at low temperature (60°C) in 0.5% CaCl2 solution for 20 or 30 min followed by blanching at high temperature (~98°C) in boiling water for 5 or 10 min was effective in potato strips processing to improve color and textural quality. However, optimal quality varies based on customer preferences. Moreover, hot water blanching is also necessary for surface pasteurization of potato strips. However, microbial recontamination and resulting growth will occur unless a proper environment is provided during packaging. Near-aseptic packaging was found to be an alternative non-chemical method to extend shelf-life of blanched potato strips. In near-aseptic packaging of potato strips, blanched and cooled strips are packaged in a near-aseptic environment in which the packaging chamber and packaging materials are pasteurized with steam at atmospheric pressure for 30 min, then cooled to room temperature and continuously pressurized with filter sterilized air. In this part of the study, the effect of low (60°C) and high (~98°C) temperature blanching time and storage time on microbial, color and textural quality of near-aseptically packaged refrigerated potato strips were examined. Microbial spoilage was observed for all treatments which received a high temperature blanch of only one minute. No microbial growth was observed within 28 days of refrigerated storage for strips treated for either 10- or 20-min in low temperature blanch followed by 5- or 10-min in high temperature blanch. Near-aseptically packaged refrigerated potato fries were lighter in color (P < 0.05) than unprocessed fries (neither blanched nor near-aseptically packaged) and less color difference (P < 0.05) was observed in near-aseptic potato fries compared to unprocessed fries. Near-aseptic potato fries were higher in peak force (P < 0.05) compared to unprocessed fries. No significant changes were observed in the quality of near-aseptically packaged refrigerated potato strips during 28 days of storage at 7°C. Gaseous ozone, a strong antimicrobial agent, was studied as an in-package treatment of blanched potato strips to extend shelf-life. Potato strips were subjected to a batch ozone treatment for 20 s or a continuous ozone treatment for 5, 15 or 30 min by injecting ozone gas into the package. Microbial growth was observed the following day for bags with no ozone treatments. Continuous ozone treatment was effective in extending shelf-life of refrigerated potato strips compared to batch ozone treatment. No microbial growth was observed in 30- and 15-min continuous ozone treated strips after 28 and 21 days storage, respectively. There was no significant difference between the color of blanched strips and ozone treated blanched strips. Finally, using the best treatments for the earlier experiments, the effects of near-aseptic packaging and in-package chemical treatments with gaseous ozone, sodium metabisulfite (SM) solution and FIT Fruit and Vegetable Wash™ solution on 2-step blanched potato strips were investigated. There was no microbial growth on any of the potato strips during 28 days of refrigerated storage. In SM treated strips, lighter color (P < 0.05) and less color difference (P < 0.05) were observed after frying compared to other treatments. Near-aseptic packaging was found to be an effective non-chemical alternative because there was no significant difference in before-frying color, textural quality and oil content compared to SM treatment which is currently the industry practice. FIT was found to be the most effective chemical treatment because the FIT significantly increased after-frying peak force of fries. Gaseous ozone treatment significantly decreased the color quality of potato strips. There was no significant difference in the oil content of near-aseptically packaged potato fries, in package chemically treated potato fries and unprocessed fries. Overall, the research results indicate that two-step blanching is necessary in improving color and textural quality of potato strips. Near-aseptic packaging as a non-chemical treatment and in-package FIT treatment are the better alternatives for blanched potato strips to extend shelf-life and maintain quality.