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Peter M.A. Toivonen

The research was conducted to first determine the commercial reality in regards to effectiveness of hydrocooling of sweet cherries (Prunus avium) at commercial packing houses. Temperature data obtained from the commercial studies were then used as a guide to evaluate the effect of small differences (0.5, 3, and 5 °C) in sweet cherry core temperature on the quality retention of ‘Sweetheart’ sweet cherries over 6 weeks of storage to simulate container shipment. Sweet cherry core temperatures after in-line hydrocooling and at the time of packing were generally around 3 or 5 °C. Once palletized and placed in commercial cold rooms, the internal boxes of a pallet did not cool any further. Only when a pallet was exposed to direct airflow from cooling coils did the exterior boxes in an assembled pallet show any further reduction in core temperature of packed sweet cherries. Experiments to evaluate the differences in quality retention at close to ideal core temperature (0.5 °C) vs. at more typical 3 or 5 °C core temperatures demonstrated significant decline when the two higher temperatures were maintained over 6 weeks of storage. Sweet cherry firmness, titratable acidity, and stem removal force value declines in storage were significantly affected by these small differences in core temperature, showing the best retention at 0.5 °C. Stem browning increased significantly with 3 or 5 °C storage by 6 weeks of storage. Decay was also significantly increased with warmer temperatures, but the results were variable likely due to differences in fruit infection at the time of harvest. Soluble solids were unaffected by storage temperature, and weight loss and pitting severity were somewhat affected. These results support the need for post packing cooling of sweet cherries as the core temperatures achieved by in-line hydrocoolers during packing do not reduce temperatures sufficiently to ensure good quality retention over longer periods of time that are required for container shipping to export markets. Therefore, forced-air cooling is recommended to further reduce sweet cherry temperatures in the box, before shipping.

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Peter M.A. Toivonen

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Peter M.A. Toivonen

The application of 1-methylcyclopropene (1-MCP) in fresh-cut processing systems has been approached in three ways: 1) treatment of freshly harvested crop before longer-term storage after which the product is processed, 2) treatment of whole product just before processing, or 3) treatment of fresh-cut product immediately after processing. Results in the literature to date are quite variable in terms of whether 1-MCP treatment provides a benefit, no effect, or a negative effect on shelf life and quality retention of fresh-cut product. There are a number factors that impact the nature and extent of response to 1-MCP by fresh product and these include, but are not limited to, temperature of storage for fresh-cut product, condition of raw product, type of fruit or vegetable, cultivar, harvest maturity, duration of storage before cutting, and the 1-MCP treatment approach. A critical analysis, using existing published and unpublished data, provides a preliminary assessment of the impact of some of these factors. This analysis is intended to provide some insight into important considerations on the use of 1-MCP in fresh-cut processing systems and will guide researchers in considering experimental parameters for future work.

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Peter M.A. Toivonen

Chlorophyll “a” fluorescence (Fvar) was compared with respiration and vitamin C content of broccoli [Brassica oleracea L. (Botrytis group)] during storage at 1C. The amplitude of the Fvar maxima declined in a similar manner as respiration and vitamin C content. Fvar was highly correlated with respiration (r = 0·83, P > = 0·0001). The correlation of Fvar with vitamin C content was weaker (r = 0·42, P > = 0·0002). The results demonstrate that Fvar is an indicator of postharvest changes in broccoli and that Fvar can be used as a nondestructive indicator of early changes in tissue condition (i.e., degree of freshness) of broccoli in storage.

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Peter M.A. Toivonen and Pascal Delaquis

Use of sprays to sanitize and treat apple (Malus ×domestica) slices helps to reduce the potential for cross-contamination that can occur when treatments are done in dip tanks. This research examined several factors that may affect the efficacy of spray treatments: 1) spray volume; 2) efficacy of spray application of anti-browning solution (ABS) compared with dipping; 3) effect of slice density during spraying; and 4) effect of the addition of an antimicrobial compound, vanillin, on microbiologically associated browning. Low-volume sprays (36-50 mL·kg-1 slices) of ABS gave maximal control of browning and this was equivalent to the control afforded by a 2-minute dip in the ABS. Spray application resulted in significant reduction in incidence and severity of microbiologically associated “secondary browning” as compared with dip application. However, if more than one layer of slices were present on the support mesh during the spray treatment, then secondary browning increased. This was attributed to potential cross-contamination between layers of apples in the spray treatment. Addition of vanillin into the ABS resulted in a 50% reduction of the incidence of “secondary browning.” Low-volume spray applications of ABS can be managed such that the microbiologically associated “secondary browning” is much lower than possible with dip application.

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Jennifer R. DeEll and Peter M.A. Toivonen

The objective of this study was to determine if chlorophyll fluorescence could be used as an indicator of anaerobic respiration in broccoli (Brassica oleracea L., Italica group) during modified-atmosphere packaging (MAP). Two types of packages were used, PD-941 bags, which provided optimum MAP conditions for broccoli (≈3 kPa O2 plus 5 kPa CO2), and PD-961EZ bags, which allowed the CO2 to accumulate (≈11 kPa CO2). After 28 days in MAP at 1 °C, the broccoli from both types of bag had similar appearances and weight losses. However, broccoli held in the PD-961EZ bags had developed slight to moderate alcoholic off-odors and had higher ethanol, acetaldehyde, and ethyl acetate content, as compared with broccoli in PD-941 bags. Chlorophyll fluorescence parameters (Fv/Fm, T1/2, Fmd, and ΦPSII) were lower for broccoli held in the PD-961EZ bags than in PD-941 bags, and these differences increased with storage duration. These results indicate that chlorophyll fluorescence is a reliable, rapid, nondestructive indicator of broccoli quality during MAP, and that it could be used to determine if broccoli has developed off-odors without opening the bag and disrupting the package atmosphere.

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Margaret A. Cliff, Kareen Stanich and Peter M.A. Toivonen

The splitting of sweet cherry (Prunus avium L.) just before harvest can be a considerable problem in the Okanagan Valley (BC, Canada). In an attempt to minimize economic losses, growers apply a commercial cherry cuticle supplement in anticipation of a rainfall event. However, it is unknown if this product affects flavor, texture (crispness, firmness, and juiciness), or visual characteristics (stem browning, pitting, and pebbling) of sweet cherry. Therefore, this research was undertaken to evaluate the effects of a cherry cuticle supplement on the sensory, physicochemical, and visual characteristics of ‘Skeena’ sweet cherry. Firmness measurements were assessed with a fruit-firmness tester, whereas sensory determinations were assessed at first bite (whole-cherry crispness) and after multiple chews (flesh firmness) by a panel of 14 trained panelists. Fruit treated with the cherry cuticle supplement had lower instrumental firmness compared with the control, which was most pronounced after 28 days, with a reduction of 0.53 N. Treated fruit also had significantly lower sensory firmness and higher juiciness than the control fruit. Fruit treated with the cherry cuticle supplement had reduced water loss, less pitting, and lower stem-pull force, resulting in higher frequency of detachment of the stems. Further research would be necessary to evaluate the effects with other cultivars, and in years with rainfall events, as well as when hydrocooling is used.

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Solomon I. Shibairo, Mahesh K. Upadhyaya and Peter M.A. Toivonen

Replacing postharvest moisture loss in carrots (Daucus carota L., `Caro-choice') by single and repeated recharging (rehydration in water) treatments, interaction between the duration of recharging and temperature during recharging, and the effects of these treatments on moisture loss during subsequent short-term storage were studied. Carrot mass gain increased with increase in duration of single recharging treatments. Carrots that had lost 2.96% of their mass during storage at 13 °C and 35% relative humidity regained as much as 83% of the mass during recharging for 12 hours. Longer rechargings had little additional effect. Recharging at 13 °C and 26 °C was more effective at replacing water than at 0 °C. The rate of moisture loss (percent per day) during subsequent storage was not affected by recharging duration and temperature during recharging. With repeated recharging every 3.5 days, increase in recharging duration up to 9 hours increased carrot mass gain. Most of the mass gain occurred following 0 to 7 days of storage. These treatments, however, did not affect the rate of moisture loss during subsequent storage. These results suggest that the beneficial effect of recharging on carrot quality is due to replacement of the lost moisture and not to a decrease in moisture loss during storage following recharging. Abrading increased mass loss in non-recharged carrots and increased mass gain during recharging. Recharging should be explored as an option to improve the shelf life of carrots.

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Yiping Gong, Peter M.A. Toivonen, O.L. Lau and Paul A. Wiersma

Apple fruits (Malus domestica Borkh. cv. Braeburn) harvested from two orchards (A and B) on the same day were stored in air or pretreated in air for 0, 2 (2dCA) or 4 weeks (4dCA) before moving into controlled atmosphere (CA) storage with 1.5% O2 + 5% CO2. During storage at 1 °C for 9 weeks in air and/or CA, changes of pyruvate decarboxylase (PDC) activity, alcohol dehydrogenase (ADH) activity, acetaldehyde (AA) and ethanol (EtOH) concentrations in flesh tissue were assayed in addition to the incidence of Braeburn browning disorder (BBD). Immediate introduction to CA conditions induced the development of BBD with the highest incidence 62.2%, however delaying application of CA for 2 and 4 weeks reduced the incidence of BBD to 38.5% and 27.0%. The development of disorder in grower B was less than in grower A. 2dCA and 4dCA treatments did not influence PDC activity compared with treatment of CA. However, ADH activity and the accumulation of AA and EtOH in treatments of 2dCA and 4dCA were markedly lower than those in CA. The accumulation of AA in grower B was lower than grower A. The results of this study suggest that the delayed application of CA reduced BBD and this may be due to reduced anaerobic metabolism of fruits in the delayed CA.

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Peter M.A. Toivonen, Jared Stoochnoff, Kevin Usher, Changwen Lu, Paul A. Wiersma and Chunhua Zhou

The market value of the apple (Malus ×domestica Borkh.) cultivar Ambrosia is closely linked to the characteristic blush on the skin surface. For ‘Ambrosia’ orchards that produce consistently low levels of surface blush, the implementation of reflective rowcovering has improved surface coloration, but the reflected wavebands responsible for this enhanced color production have not been confirmed. This study consisted of two separate experiments: one conducted in the field to confirm reflective rowcovering efficacy and the other in a controlled environment cabinet to determine which waveband was enhancing red blush production. The red blush production in orchards with and without reflective rowcovering was then directly compared with the red blush produced on the surface of apples that were poorly colored at harvest and then exposed to visible, fluorescent, ultraviolet A (UVA), or ultraviolet B (UVB) light sources within the controlled environment chamber. Consequent analysis of the red blush color within the Commission Internationale de l’Eclairage a* and b* color space was conducted to evaluate the quality of the red blush pigment under each treatment in the field and the controlled environment chamber. The analysis revealed that the red blush that developed on apples from the reflective rowcover treatment most closely matched the red blush that developed in response to UVB exposure in the controlled environment cabinet. Further analysis of gene expression and anthocyanin contents in the ‘Ambrosia’ apples support the hypothesis that the primary driver for the characteristic red blush development, when reflective rowcovers are used, is increased exposure to UVB light.