Peter M.A. Toivonen

Practical applications of chlorophyll fluorescence in plant biology

Preface. List of Figures. List of Tables. Chlorophyll Fluorescence Nomenclature. 1. An Introduction to Chlorophyll Fluorescence J. Harbinson, E. Rosenqvist. 2. Chlorophyll Fluorescence: A General Description and Nomenclature E. Rosenqvist, O. van Kooten. 3. Applications of Chlorophyll Fluorescence in Forestry and Ecophysiology G.H. Mohammed, P. Zarco-Tejada, J.R. Miller. 4. The Application of Chlorophyll Fluorescence to Study Light, Temperature, and Drought Stress Y. Fracheboud, J. Leipner. 5. Applications of Chlorophyll Fluorescence in Ecotoxicology: Heavy Metals, Herbicides, and Air Pollutants R. Popovic, D. Dewez, P. Juneau. 6. The Application of Chlorophyll Fluorescence in the Aquatic Environment C. Wilhelm. 7. Use of Chlorophyll Fluorescence in Postharvest Quality Assessments of Fruits and Vegetables J.R. DeEll, P.M.A. Toivonen. 8. The Potential of Chlorophyll Fluorescence in Fruit Breeding S. Khanizadeh, J.R. DeEll. Index.

Antilisterial activity of selected phenolic-acids

Phenolic acids are known to exhibit antimicrobial activity against a variety of micro-organisms. Their influence on the behavior of Listeria monocytogenes, particularly in foods derived from plants, is not well understood. Several phenolic acids including chlorogenic acid and the hydroxycinnamic acids, caffeic acid, p-coumaric acid and ferulic acid, were screened for activity against five strains of L. monocytogenes using a broth dilution method. Minimum inhibitory concentrations ranged between 0.20% and 0.27% (w/vol) for the hydroxycinnamic acids, but chlorogenic acid was ineffective at 1.0% (w/vol). Mixtures of the acids generally exhibited additive antilisterial effects in a checkerboard assay. Growth experiments performed at pH 4.5, 5.5 and 6.5 revealed a strong relationship between pH and activity. All the hydroxycinnamic acids were bactericidal at pH 4.5 and bacteriostatic at higher pH. In contrast, chlorogenic acid inhibited growth of L. monocytogenes only at pH 6.5. The implications of these finding for the ecology of the species in foods are discussed.

Effect of warm, chlorinated water on the microbial flora of shredded iceberg lettuce

Abstract An optimization technique was used to determine suitable times of exposure and temperatures for maximum destruction of microorganisms in shredded iceberg lettuce dipped in warm, chlorinated (100 μg/ml) water in a model system. Shredded lettuce washed for 3 min at 47°C and packaged in high oxygen transmission rate (6000–8000 cc m2 24 h) bags maintained an acceptable appearance after 7 days in storage at 1±1°C. Initial microbial loads were reduced by approximately 3 log cfu g−1 in lettuce washed in chlorinated water at 47°C, and 1 log cfu g−1 at 4°C. Pilot plant scale studies confirmed observations in the model system. The microbial flora of shredded lettuce packaged in the raw state and after a 3 min wash in 100 g ml−1 chlorine at 4 or 47°C was dominated by psychrotrophic bacteria, particularly species of Pseudomonas, throughout the storage period. Numbers of these microorganisms were significantly lower than in raw lettuce or lettuce washed at 4°C until the 15th day in storage. Gas composition inside the bags was not affected by the washes.

Survival and growth of Listeria monocytogenes and Escherichia coli O157:H7 in ready-to-eat iceberg lettuce washed in warm chlorinated water.

Cut iceberg lettuce inoculated with Escherichia coli O157:H7 and Listeria monocytogenes before and after washing for 3 min in cold (4 degrees C) and warm (47 degrees C) water containing 100 mg/liter total chlorine was stored at I and 10 degrees C in oxygen-permeable film packages (6,000 to 8,000 cc/m2/24 h). Cold chlorinated water was detrimental to the survival of E. coli O157: H7 and L. monocytogenes at both storage temperatures. In contrast, washing in warm chlorinated water favored the growth of both pathogens in lettuce stored at 10 degrees C. There was no evidence of a relationship between the magnitude of spoilage microflora and the fate of either bacterium.

Effect of pH on the inhibition of Listeria spp. by vanillin and vanillic acid.

The antimicrobial effects of vanillin and vanillic acid were verified against several species and strains of Listeria monocytogenes, Listeria innocua, Listeria grayi, and Listeria seeligeri in a laboratory medium adjusted to pH values ranging from 5.0 to 8.0. Medium pH had little influence on the MIC of vanillin as determined by a broth dilution assay, and growth of all test strains was inhibited by concentrations ranging from 23 to 33 mM. In contrast, none of the strains were inhibited by 100 mM vanillic acid at pH > 6.0, but complete inhibition was achieved at pH 5.0 with 10 mM. The effect of pH was further characterized by incubation of L. monocytogenes, L. innocua, and L. grayi in media containing 30 mM vanillin or 60 mM vanillic acid at pH 5.0, 6.0, and 7.0. Bactericidal effects increased with pH in media supplemented with vanillin. An inverse relationship was found for vanillic acid, and the lethality of the compound increased with declining pH. Mixtures of vanillin and vanillic acid exhibited additive inhibitory effects, particularly at lower pH. These natural antimicrobial compounds could prove useful either alone or in mixtures for the control of Listeria spp. in food products.

Non-ethylene, non-respiratory volatiles in harvested fruits and vegetables: their occurrence, biological activity and control

Abstract This review examines the occurrence of organic volatiles which may have physiological and/or quality effects on fresh produce. Accumulations of terpenes, carboxylic acids, alcohols, aldehydes, sulfur compounds, ammonia and jasmonates are discussed. Factors influencing volatile accumulation are considered. Conventional approaches for removing volatiles are evaluated and an approach involving enhanced product transpiration is proposed. A hypothesis regarding this modified, selective approach to volatiles control is presented. In summary, it is concluded that further work on effects of non-ethylene volatiles is needed and selective approaches to volatile removal be developed.

The effects of storage temperature, storage duration, hydro-cooling, and micro-perforated wrap on shelf life of broccoli (Brassica oleracea L., Italica Group)

Abstract This work was initiated to determine the effects of cold storage duration and storage temperature on the shelf life of wrapped broccoli when subsequently placed into elevated temperatures to simulate retail shelf conditions. In addition, the effect of hydro-cooling prior to wrapping was evaluated. These tests were designed to test the potential for micro-perforated wrap in extending shelf life of broccoli under varied postharvest handling conditions. In the first experiment, broccoli (Brassica oleracea L., Italica Group; cv. Mariner) was harvested and the crop divided into 4 treatments; (1) ‘hydro-cooled + no wrap’, (2) ‘hydro-cooled + wrap’, (3) ‘non-cooled + no wrap’, and (4) ‘non-cooled + wrap’. Samples of each of the 4 treatments were removed from storage after 3 days at 1 °C and placed into 13 °C to simulate shelf conditions. Visual quality, weight loss and respiration were monitored over 5 days at 13 °C. This shelf evaluation was repeated with broccoli samples that had been stored for 10 and 17 days at 1 °C. In a second experiment, broccoli was harvested and hydro-cooled. Half the crop was wrapped with micro-perforated film and the other half left unwrapped. From these two treatments, half of the heads were stored at 1 °C and the other half at 5 °C. After 10 days, all the heads were placed at 13 °C for 5 days. Measurements at 13 °C were taken as in the first experiment. In the first experiment, for broccoli which was stored for only 3 days at 1 °C, the use of either hydro-cooling or wrap gave good firmness retention at 13 °C shelf conditions. However, for broccoli which had been stored for 10 or 17 days, both hydro-cooling and wrapping were required to achieve the best firmness retention. Yellowing during the 5 days at 13 °C was found to be the greatest for broccoli that had been stored at 1 °C for only 3 days. Broccoli stored for 10 and 17 days developed much less yellowing during 5 days holding at 13 °C. In the second experiment, storage at 1 °C resulted in much better shelf life than storage at 5 °C. Application of wrap gave best firmness retention and least water loss, independently of storage temperature. Only colour retention was affected by storage temperature, with 5 °C storage resulting in a significant increase in yellowing. Neither hydro-cooling nor packaging had an effect on yellowing. Therefore, broccoli firmness and colour retention can be easily maintained for 5 days at elevated ‘shelf’ temperatures with the integration of a system which includes hydro-cooling, application of micro-perforated film wrap and sufficient cold storage duration at 1 °C.

Chlorophyll fluorescence, fermentation product accumulation, and quality of stored broccoli in modified atmosphere packages and subsequent air storage☆

Abstract Earlier work showed that chlorophyll fluorescence changes of broccoli (Brassica oleracea L., Italica group) were associated with the accumulation of CO2 in modified atmosphere packages (MAP) during storage. This work was initiated to determine whether the chlorophyll fluorescence changes in broccoli from high CO2 MAP are persistent after the packages are opened and the broccoli is allowed to aerate. PD-961EZ bags, which allow the CO2 to accumulate (∼11 kPa CO2), were used in this study. During 28 days in MAP at 1°C, the broccoli gradually developed slight to moderate alcoholic off-odors and accumulated ethanol, acetaldehyde, and ethyl acetate in the tissues. These levels dissipated slightly on opening of the bags and holding the broccoli in 1°C air storage for 4 days. Chlorophyll fluorescence measurements (Fv/Fm, T 1 2 , Fmd, and ΦPSII) declined for broccoli with the accumulation of these anaerobic products and the fluorescence measurements recovered slightly after the bags were opened and the broccoli was held in air at 1°C for 4 days. Chlorophyll fluorescence measurements were found to be highly correlated with the anaerobic volatile content in broccoli during MAP storage and after opening of the MAP. Chlorophyll fluorescence measurements were also highly correlated with the perceived off-odors that were noted for the broccoli after longer storage durations in MAP.

Effect of 1 and 100 kPa O2 atmospheric pretreatments of whole ‘Spartan’ apples on subsequent quality and shelf life of slices stored in modified atmosphere packages☆

Abstract Whole ‘Spartan’ apples were exposed to 1 kPa O2, air (21 kPa O2) and 100 kPa O2 at 1°C for 5, 12 and 19 days. Subsequent to the pretreatment, apples were cored, sliced and 400±5 g of slices were sealed in 40-μm-thick low density polyethylene film bags having a moderate O2 transmission rate (OTR∼2.28 fmol s−1 m m−2 Pa−1 at 23°C) and held for up to 2 weeks at 1°C. Cut surface browning and flesh softening were inhibited for packaged slices by pretreating the whole fruit with 100 and 1 kPa O2 as compared with those from the air pretreatment. However the slices from the 100 kPa O2- and air-pretreated apples contained a much lower content of fermentation products associated with off-flavors compared with the slices from apples pretreated in 1 kPa O2. Packages containing apple slices from the air pretreatment developed a more highly modified atmosphere than packages containing apples slices from the other two pretreatments, suggesting that both 1 and 100 kPa O2 pretreatments suppressed the respiration rate of apple slices. Slices from apples pretreated with 1 kPa O2 developed more cut surface browning and greater tissue solute leakage and enhanced accumulations of acetaldehyde, ethanol and ethyl acetate in apple slice tissue as compared with slices cut from the 100 kPa O2-pretreated apples.

Antimicrobial activity of vanillin against spoilage microorganisms in stored fresh-cut mangoes

The antimicrobial activity of vanillin against four bacteria (Pantoea agglomerans, Aeromonas enteropelogenes, Micrococcus lylae, and Sphingobacterium spiritovorun), four fungi (Alternaria sp., Aspergillus sp., Penicillium sp., and Fusarium sp.), and three unidentified yeasts isolated from spoiling fresh-cut mango slices was verified in laboratory media adjusted to pH 5.0. MICs of vanillin against the fungi (12.5 to 13.3 mM), bacteria (10 to 13.3 mM), and yeasts (5.0 to 6.7 mM) indicated that all the test species were sensitive to the antimicrobial effects of vanillin. Fresh-cut mango slices were dipped for 1 min in solutions containing 40 and 80 mM vanillin before being packaged in rigid trays and stored at 5 and 10 degrees C to verify the effects of vanillin on the development of the spoilage microflora. Microbiological analysis for up to 14 days of storage revealed that treatment with 80 mM vanillin significantly delayed (P < 0.05) the development of total aerobic bacteria and yeast and mold populations. Vanillin may be a practical preservative for processing fresh-cut mango.