Wpływ warunków uprawy oraz obróbki cieplnej na zanieczyszczenie mikrobiologiczne i inne wybrane wskaźniki jakości kiełków nasion

Magdalena Michalczyk

Abstract

Sprouted seeds are a sensorially pleasant dietary component rich in a number of biologically valuable substances. Many studies have shown that sprouting reduces the levels of undesirable substances such as phytic acid and tannins, while increasing levels of health-promoting constituents such as vitamin C and glucosinolates, including sulphoraphane. Simultanousely, sprouts carry a high load of microorganisms,frequently exceeding 108 - 109 cfu/g. There are documented cases of foodborne infections coused by Salmonella and Escherichia coli O157:H7 after the consumption of sprouted seeds. Thus, the decontamination of seeds prior to sprouting is strongly recomended. However, many studies dealing with this issue suggest that so far applied procedures are not totally effective. Furthermore, the use of calcium hypochlorite or sodium hypochlorite solutions has caused concern over their possible negative effects on human’s health. The lack of a satisfactory method of decontamination of sprouts cause that thermal treatment prior to consumption is sometimes recommended. The aim of this work was to evaluate the effect of seed decontamination and modified sprouting methods on microbiological contamination of sprouts. In addition, the effect was investigated of selected methods of thermal treatment of sprouts on their contamination by microorganisms and on the levels of biologically active constituents such as vitamin C, polyphenols, chlorophylls and carotenoids. Research area was divided into 8 experiments. In experiments I and III, in successive days of growing, two sprouting methods: tray and immersion method were compared in terms of their effect on the microbial contamination of sprouts. During experiments II, IV, VI, and VII, the efficacy was evaluated of disinfection procedures applied both to seeds and throughout the whole sprouting period. In the experiment V, the possible application of the Lactobacillus plantarum strain was estimated in order to model the composition of microorganisms on sprouts. In addition, an effect has been evaluated of heat treatment of sprouts on their microbiological contamination and the content of selected bioactive constituents (experiment VIII). Microbiological analyses, which were conducted throughout experiments, included determination of total viable count (TVC), Enterobacteriaceae count, moulds, yeasts and lactic acid bacteria (LAB) count. In addition, with regard to part of the experimental work, the mass of 100 sprouts was determined as well as the contents of vitamin C, chlorophylls, carotenoids, and total phenolic content. Radish seeds were used to analyse the effects of decontaminant solutions due to their popularity and observed reproducibility of microbiological characteristics. Among the solutions used in the experiments II and VII were calcium hypochlorite, chlorine dioxide, silver nitrate(V), potassium permanganate, hydrogen peroxide, propolis and cranberries extract. No reduction in microorganism counts was achieved by any of the decontaminants used on seeds prior to and during sprouting on trays. Moreover, thermal treatment of seeds (at 62°C, 70°C or 90°C) prior to germination did not lower the level of microbiological contamination of the sprouts (experiment VI). Although the use of antimicrobial solutions, such as calcium hypochlorite (20 000 ppm active chlorine), and 250 ppm chlorine dioxide (experiment VII), or the application of thermal treatment did reduce levels of microbiological contamination on the seeds, they did not reduce levels of microorganisms on the resulting sprouts. This can be attributed to the rapid proliferation of that microorganisms remaining on the seeds after decontamination as well as to partial damage to the subsequent sprouts, which compromised the plants’ own defence mechanisms. In radish sprouts obtained from seeds decontaminated with calcium hypochlorite (20 000 ppm active chlorine), the root apex was frequently observed to have died, with SEM images showing intensive microorganism concentrations as biofilm on the dead tissue. Decontamination with chlorine solutions (20 000 ppm active chlorine as calcium hypochlorite, 250 ppm chlorine dioxide) and thermal treatment (at 62°C, 70°C and 90°C) of radish seeds resulted in significant decreases in vitamin C and in most cases a significant increase in the content of total polyphenols in the resulting sprouts compared with the control sample, which is further evidence of partial damage to the raw material caused by the treatments applied. The modified sprouting method was evaluated by comparing microbiological contamination in sprouts germinated using the immersion method with contamination in sprouts obtained using commercial tray sprouters. Immersion sprouting was carried out in mesh containers totally immersed in water tanks into which air was pumped through an airstone connected to a diaphragm pump. Seeds of radish, broccoli, wheat, mung bean, red cabbage, pumpkin, lentil and lucerne were germinated in trays. Mung bean, pumpkin and lentil seeds were excluded from immersion sprouting because growth of these species was inhibited. The characteristics of microorganism proliferation were very similar in sprouts obtained by both the tray and immersion methods, the most rapid proliferation occurring after the first 24 h. After 48 h the microorganism count was close to the maximum recorded of 108 - 109 cfu/g; the level of contamination of the seeds themselves was not a factor in these results. Contamination was lower in sprouts obtained by the immersion method than in the corresponding sprouts germinated in trays; however, the difference was generally not greater than one logarithmic cycle. Since the immersion method enables constant exposure of the seeds to the substances contained in the solutions applied, plant extracts with known antimicrobial properties were tried as bacteriostatic agents (experiment IV). Thus, radish seeds were sprouted in solutions containing extract of garlic, horseradish, grapefruit seed, ginger or hops. No reduction in microbiological contamination was found in any of the experiments carried out; moreover, yields were distinctly lower, and in some cases damage to sprouts was observed. In additional samples, where the extracts were applied directly to the growth media on which microorganisms isolated from the control sprouts were grown, only in the case of garlic extract was there any distinct reduction in the number of bacteria, yeasts and moulds; however, with the exception of moulds, this was not reflected in the sprouts themselves. A similarly disappointing result was achieved when radish seeds were inoculated with Lactobacillus plantarum (107 cfu/g). The aim was to increase the proportion of lactic acid bacteria in the total microorganism count in the sprouts. However, this did not occur and no reduction in the levels of the native microorganisms under investigation was found; moreover, there was a decrease in the mass of the resulting sprouts. In experiment VIII radish, lucerne, wheat, lentil, mung bean and broccoli sprouts underwent thermal treatment by steaming for 2 min or immersing for 10 sec in water at 100°C or ≥90°C. In all cases, there was a reduction in Enterobacteriaceae and moulds counts below the detectable levels as well as an essential decrease in TVC of 2 to 5 logarithmic cycles and 5–7 logarithmic cycles in yeasts. At the same time, these processes led to losses of vitamin C, chlorophyll, carotenoids and polyphenols, the losses being smaller in sprouts immersed in hot water than in those which were steamed. The results obtained in this study indicate that decontamination of seeds either prior to or during sprouting is ineffective in limiting microbiological contamination. Moreover, such procedures, depending on the agent used or its concentration, may result in lower yields and damage to the sprouts, impairing the plants’ defence mechanisms and affecting levels of active biological constituents in the sprouts.
Other language title versionsEffect of growing conditions and thermal treatment on microbiological contamination and other selected quality indicators of sprouted seeds
Book typeMonograph
Other categories ROZPRAWA_HABILITACYJNA
Author Magdalena Michalczyk (FoFT / DoRaFC)
Magdalena Michalczyk,,
- Department of Refrigeration and Food Concentrates
PublisherUniwersytet Rolniczy im. Hugona Kołłątaja w Krakowie, MNiSW [80]
Publishing place (Publisher address)Kraków
Issue year2015
Book series /Journal (in case of Journal special issue)Zeszyty Naukowe Uniwersytetu Rolniczego im. Hugona Kołłątaja w Krakowie. Rozprawy, ISSN 1899-3486, (0 pkt)
Vol528
No405
Pages102
Publication size in sheets10
Internal identifierWRE/12/64
Languagepl polski
File
Wpływ warunków uprawy oraz obróbki cieplnej na zanieczyszczenie mikrobiologiczne i inne wybrane wskaźniki jakości kiełków nasion 11,25 MB
Score (nominal)25
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