Graduate Thesis Or Dissertation


The effect of physical and chemical agents on the storage characteristics of raw vegetables and fruits Public Deposited

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  • This investigation was concerned with the reduction of waste in raw vegetables and fruits between the times of harvest and consumption. Reduction of spoilage in produce was attempted by means of chemical and. physical agents as well as a combination of both. The first phase of the work consisted of an evaluation of a number of chemical compounds with respect to their effectiveness in reducing post-harvest spoilage. The second part dealt with an evaluation of several transparent films applied to raw produce as wrappers and their effect on the keeping quality of the plant material until consumed. Finally combinations of surface disinfection and overwrapping were evaluated for effectiveness against raw produce spoilage. 1. Disinfection Approximately 26 compounds were tested as aqueous dips using 3 concentrations of each on 7 major vegetables and 2 fruits. The following types of compounds were studied. 1. Quaternary ammonium compounds (chlorides, bromides and pyridinium derivatives) 2. Chlorine liberators (organic and inorganic) 3. Phenols (simple and poly-phenols) 4. Quinones and hydroquinones 5. Salts of fatty acids 6. SO₂ liberators 7. Benzoates The chemical treatments were evaluated for each produce by comparison with untreated controls using duplicate tests with triplicate samples for each chemical and concentration. Promising treatments were found for all but one produce (strawberries). The treatments showing promise for each of Pascal celery and Emperor grapes were further tested on a larger scale uaing commercial size units of produce as test samples and long term cold storage. Three chemical treatments for each product were judged satisfactory enough to warrant further testing by means of field trials. The chemicals found most promising for celery were Onyxide, Cetab and Decco while Roccal, Dowicide C and Phygon were selected for grapes. A field test of the three above mentioned treatments for Pascal celery was completed. One thousand bunches per chemical were tested under commercial conditions of dipping and storing. An equal number of untreated bunches was also tested. Half-lots of each treatment were evaluated on each bunch for 11 subjective characteristics and standard mold and bacterial counts of each crate of celery were made after 8 and 14 weeks of storage. On the basis of a statistical analysis of the results, 0.1% Decco of pH=5 can be recommended for the reduction of general rot development in cold storage Pascal celery. Onyxide and Cetab significantly reduce the development of mold but commercial application cannot be recommended because the amount of visible stalk injury was significantly increased over that shown by corresponding untreated or Decco treated celery. 2. Prepackaging The following films were compared for their merit in prolonging the salable life of raw produce. Pliofilm 75FF, Pliofilm 75N2, Pliofilm 75P6A, Cellophane 300LSAT, Cellophane 300MSAT-86, Lumarith P-912, Dupont Acetate 100CA48, Polythene and Kodapak II-130. Wrapping techniques were also evaluated using the followng variations; Complete seals, tent-flap closures, single hole punctures, multiple punctures and windo bags. The following products were studied: celery, tomatoes, carrots, lettuce, cauliflower, chopped salad mix, spinach, strawberries, raspberries, blackberries, and boysenberries. Harvested produce was packaged both before and after the removal of field heat. Behavior of the pre-packaged products in both 33°F storage and subsequent 8O°F storage was studied. Cold storage was extended as long as 120 days while subsequent holding at room temperature varied widely from produce to produce. Observations were made at regular intervals for each product. Several hundred uniform samples were evaluated for most products using duplicates of each treatment for every observation period. Evaluation of most samples included weightloss, C0₂ (and sometimes O₂) of the container atmosphere, mold and decay development, flavor, color, odor, wilting and shriveling. The following conclusions were drawn: All films and wrapping methods affect produce quality. For each produce, treatments could be singled out which were superior to unwrapped controls. However any particular film and type of seal found to be superior for one produce was often not acceptable for another fruit or vegetable. Among the factors found to be critical for the proper choice of treatment were type of produce, produce temperature when packed, length of storage, and temperature of storage. A. Cold Storage For most products, the partially sealed, low permeability MSAT containers and the completely sealed Polythene wraps scored highst for overall product quality. These treatments prevented the accumulation of undesirable CO₂ while at the same time protecting the produce against weightloss and consequent wilting. For some produce, especially berries, wilting was not apparent even in high permeability films such as acetates. B. Warm Storage For produce with high respiration rates (spinach, and berries) only acetate films were acceptable as wraps. The partially sealed low permeability films maintained good quality in warm storage but the high humidity within the package was conducive to micro-organism activity. Thus, in many cases samples disinfected prior to packaging in those films improved the warm storage quality. Disinfection also improved the quality of tomatoes and chopped salad mix in acetate wraps. Of the high permeability films, no significant difference was found among the Dupont acetate, Lumarith and Kodapak II. The type of seal also did not affect the characteristics of these wraps. The low permeability films differed principally in the amount of CO₂, retained by the container during storage. The Pliofilms retained the highest C0₂, levels followed by LSAT and then MSAT Cellophane. The sealed polyethylene, the single puncture and tent flap MSAT wraps exhibited similarity, especially with respect to C0₂ accumulation. The multiple puncture low permeability wraps showed characteristics between acetates and the last mentioned group. Correlation between CO₂ accumulation and off-flavor formation could be determined for most products. Higher CO₂ levels were tolerated at short storage intervals without off- flavor formation by most products but the rate of change in CO₂ tolerance varied from produce to produce. Correlation between % weightioss and degree of wilting could also be expressed as a function of the pre-packaging treatments used. Storage infection was eliminated by all films independent of the type of seal used. It should be emphasized that only a study of the resuits and relationships discussed under each product can serve as a basis for future work and commercial application of the methods presented in this work.
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