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Time of harvest determines the postharvest quality of the common mushroom Agaricus bisporus
Postharvest Biology and Technology 16 (1999) 195 – 198
Short communication
Time of harvest determines the postharvest quality of the common mushroom Agaricus bisporus A. Braaksma *, D.J. Schaap, C.M.A. Schipper Agrotechnological Research Institute (ATO-DLO), P.O. Box 17, 6700 AA, Wageningen, The Netherlands Received 8 June 1998; accepted 22 February 1999
Abstract The effect of harvest time on postharvest quality of mushrooms (Agaricus bisporus strain U1) has been studied. Postharvest quality of mushrooms, especially percentage cap opening, is greater with later harvest times. In addition to time of harvest, the initial size of the mushroom at harvest is significantly correlated with the extent of cap opening. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Cap opening; Time of harvest; Postharvest quality; Agaricus; Mushroom; Shelf-life
1. Introduction Development of the mushroom, Agaricus bisporus strain U1, continues during postharvest storage. This development, shown as cap opening, stipe growth, growth of gills and production of spores, is the normal maturation process of the fruiting body, but comprises negative quality factors. It has been reported that some harvest practices, such as trimming the stipe, can improve the quality and shelf-life of mushrooms (Beelman et al., 1993). Since dry weight redistribution takes * Corresponding author. E-mail address: [email protected] (A. Braaksma)
place from the stipe towards the gill tissue during postharvest development (Braaksma et al., 1994), an inhibitory effect of stipe trimming upon cap opening might be possible. However, no effects on cultivar U1 are found in this respect; rather than increasing shelf-life, stipe trimming in U1 merely results in a larger decrease in dry weight in the cap tissue in favour of the gill tissue (unpublished observations). In a preliminary report, Beelman et al. (1993) reported positive effects of harvest time upon the quality and shelf-life of mushrooms, but did not provide supporting data. Our objective, therefore, was to see if there are beneficial effects of earlier harvest times upon postharvest development, with cap opening being a quality indicator.
0925-5214/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 ( 9 9 ) 0 0 0 1 9 - 8
196
A. Braaksma et al. / Posthar6est Biology and Technology 16 (1999) 195–198
2. Materials and methods Mushrooms (Agaricus bisporus) strain U1 were grown in four rectangular plots of 1.5 ×1.4 m within a larger bed of 18 × 1.4 m used for the commercial production of mushrooms. The growing chamber contained 24 beds. The mushrooms were at the second flush stage since it is generally accepted that mushrooms from this stage are more stable in quality and yield. The harvest dates were determined by the grower for each crop, because of uncertainties associated with the use of spawn and variations in the compost and growth environment. Harvest dates are uncertain until 3–4 days before harvest when the first fruiting bodies appear. There were four collections at each commercial harvest from one marked rectangular plot: 2 days and 1 day before the planned harvest, the day of the commercial harvest, and finally 1 day after the commercial harvest. On the marked rectangles, no single mushroom was harvested before the indicated time. The mushrooms were transported to the laboratory within 1 h of each harvest and stored at 20°C with RH\ 90%. They were then sorted by cap diameter into eight categories: 15 – 20, 20 – 30, 30 – 40, 40–50, 50–60, 60 – 70, 70 – 80, and \ 80 mm, and stored at 20°C ( \ 90% RH) for 3 days. The percentage of mushrooms with either an intact velum, a broken velum or an open cap (broken veil and an opening that exceeds 1 mm) were determined every 24 h. The experiment was repeated twice, with an average of 3000 mushrooms involved in an experiment. Statistical analysis was carried out with Genstat 5.3.2 (1993). The three different stages of the mushroom’s cap (‘closed’, ‘broken’ and ‘open’) represent ordinal data and therefore the three different stages of the cap are not independent. Furthermore, they represent proportions of the total number of mushrooms harvested and we can therefore assume that they follow a multinomial distribution. McCullagh and Nelder (1989) (see pp. 178 – 182 for an example) specify a suitable generalised linear model (GLM) which would be suitable to describe the effect of the explanatory variables
cap diameter and harvest time on the state of the cap during postharvest storage. The data were tested for main effects and the interaction of the explanatory variables at the 5% significance level. As the experiment was performed three times, the repetition number was also included as an effect in the model to describe the differences between the repetitions. The model was not tested for significance of the repetition effect. For each of the four different storage periods after the harvest time, submodels were created that lacked one of the terms (either main or interactive). These submodels were then compared with the full model to assess the significance of the dropped term. The significance was tested using the comparison of the mean difference of deviation with a x 2 distributed random variable.
3. Results and discussion It is important for the relevance of this study to know if the parameter used in this study (cap diameter) is proportional to the weight of the entire mushroom (a commercially important parameter). The relationship between cap diameter and weight was determined for each experiment and it was found that the weight of the mushrooms closely correlated with the square of the diameter of the cap. The level of significance r 2 was always 99% or higher, except in one case where it was 98%. When fitted to a linear function, r 2 dropped to approximately 96%. The yield of a typical subharvest from the plots on the growing beds was 70 mushrooms m − 2 on the first harvest day with a total weight of 0.38 kg m − 2. On the second day the harvest was 226 mushrooms m − 2 with a total weight of 2.0 kg m − 2; on the third day, 401 mushrooms m − 2 with a total weight of 5.2 kg m − 2 and on the fourth day, 624 mushrooms m − 2 with a weight of 13.0 kg m − 2. The effect of harvest time and the influence of initial size at harvest upon cap opening during storage was statistically analysed for all sizeclasses at each harvest day (thus one experiment consisted of 32 data sets).
A. Braaksma et al. / Posthar6est Biology and Technology 16 (1999) 195–198
Neglecting the interaction between harvest time and initial cap diameter, a close examination of the collected data showed that a smaller cap diameter was associated with less cap opening during the 3 day storage period. The main trends of the effect of harvest time showed that the earlier the mushrooms were harvested, the less cap opening occurred during the three subsequent days of storage; the smallest mushrooms (cap diameter of 15–20 mm) showed no cap opening during a 3 day storage period, irrespective of the day of harvest. A comparison of the full model with a submodel lacking the interaction term between initial cap diameter and harvest time shows that this interaction was significant irrespective of the storage period. This implies that both explanatory
197
variables, initial cap diameter and harvest time, have a significant effect on the state of the mushroom’s cap during storage. Through the three repetitions of the experiment the effect of the diameter was present at a high level of significance and its effect depended on the harvest time and vice versa. The level of significance (r 2) was 99% or higher in all cases, except for one where it was 98%. These levels of significance were at 5% confidence limits and did not change when they were recalculated at 1% confidence limits. The effect of harvest time can be clearly seen in Fig. 1(a–c), where the results of a typical experiment are shown. In Fig. 1(a), for the size-class of mushrooms with a cap diameter of 20–30 mm at harvest, it is clear that irrespective of the day of harvest, all mushrooms in this class initially had
Fig. 1. Percentage cap opening of mushrooms as affected by time of harvest and days of storage. All mushrooms were stored at 20°C and RH\90%. The cap opening is represented as percentages of the total number of mushrooms involved. The total number for each harvest day is in Section 2. The data are derived from a typical experiment: first day of harvest, white square; second day of harvest, diagonal stripes; third day of harvest, horizontal stripes and fourth day of harvest, dotted square. (a) Initial cap diameter of 20– 30 mm; (b) initial cap diameter of 30–40 mm; (c) initial cap diameter of 40 – 50 mm.
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A. Braaksma et al. / Posthar6est Biology and Technology 16 (1999) 195–198
closed caps. Even after a subsequent four day storage period, \95% of the mushrooms harvested on the first harvest day showed no cap opening. This was in contrast to mushrooms sampled on the fourth day of harvest, which had no closed caps after 4 days of storage. The mushrooms harvested on the second and third days had intermediate responses to the storage treatment. Mushrooms within one size-class but harvested on different days, were completely similar in size and appearance at the time of harvest. The cap opening of the 30 – 40 mm mushroom sizeclass during postharvest storage is shown in Fig. 1(b). These mushrooms show similar trends to those of the 20–30 mm class, except that these larger mushrooms opened their caps earlier during storage. This was particularly apparent where smaller mushrooms reached the 100% open cap stage at day 4 (Fig. 1a), whereas for the larger mushrooms (size-class 30 – 40 mm) the 100% stage was reached at day 2 – 3 (Fig. 1b). A similar trend was found in mushrooms with a cap diameter of 40 – 50 mm at harvest (Fig. 1c); the percentages of opening reached on days 2 and 3 of storage were higher than in the 20 – 30 and 30 – 40 mm sizeclasses, even when the mushrooms from the 40 – 50 mm size-class were harvested early (second and third day of harvest). This trend is stronger amongst larger mushrooms (results not shown). In spite of the fact that there is no difference in initial appearance if a mushroom is harvested earlier or later, it can be concluded that, if harvested later, cap opening occurs in a larger proportion of the mushrooms and cap opening is completed earlier during subsequent storage. The total yield of the whole growth chamber was between 10 and 12 kg m − 2. This was achieved by pre-picking mushrooms with a cap diameter of 20 – 40 mm on days 1 and 2 combined with the yield of the commercial harvest at the third day
.
itself. When all mushrooms were picked on day 2, lower yields resulted. The worst yield was 4 kg m − 2 and the best was about 6 kg m − 2. Therefore, while pre-picking results in a higher quality with respect to cap opening, it is not advisable for commercial reasons, unless the price for improved quality is correspondingly higher. From these data it can also be seen that the effect of harvest time is not linear over the four subsequent days of storage. Between the second and the third harvest day especially, there seems to be a discontinuity. It is hypothized that this is mediated by a change in an unknown hormonal signal from the mycelium. Further research is necessary to see if endogenous levels of growth regulators are involved in cap opening.
Acknowledgements The authors thank the CNC, the Dutch Mushroom Growers Organisation, for their financial support and Dr J. Harbinson for critically reading the manuscript.
References Beelman, R.B., Miklus, M.B., Mau, J.-L., Ajlouni, S.O., Simons, S.S., 1993. Selected cultural and harvest practices to improve quality and shelf-life of Agaricus bisporus. In: Chang, S., Buswell, J.A., Chiu, S.-W. (Eds.), Mushroom Biology and Mushroom Products, Proceedings of the First International Conference on Mushroom Biology and Mushroom Products, The Chinese University Press of the Chinese University of Hong Kong, pp.177 – 184 (23 – 26 August 1993). Braaksma, A., De Vrije, T., Jongen, W.M.F., Woltering, E.W.J., 1994. Aging of the mushroom (Agaricus bisporus) under post-harvest conditions. Postharvest Biol. Technol. 4, 99 – 110. McCullagh, P., Nelder, J.A., 1989. Generalized Linear Models. Chapman and Hall, London.
Short communication
Time of harvest determines the postharvest quality of the common mushroom Agaricus bisporus A. Braaksma *, D.J. Schaap, C.M.A. Schipper Agrotechnological Research Institute (ATO-DLO), P.O. Box 17, 6700 AA, Wageningen, The Netherlands Received 8 June 1998; accepted 22 February 1999
Abstract The effect of harvest time on postharvest quality of mushrooms (Agaricus bisporus strain U1) has been studied. Postharvest quality of mushrooms, especially percentage cap opening, is greater with later harvest times. In addition to time of harvest, the initial size of the mushroom at harvest is significantly correlated with the extent of cap opening. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Cap opening; Time of harvest; Postharvest quality; Agaricus; Mushroom; Shelf-life
1. Introduction Development of the mushroom, Agaricus bisporus strain U1, continues during postharvest storage. This development, shown as cap opening, stipe growth, growth of gills and production of spores, is the normal maturation process of the fruiting body, but comprises negative quality factors. It has been reported that some harvest practices, such as trimming the stipe, can improve the quality and shelf-life of mushrooms (Beelman et al., 1993). Since dry weight redistribution takes * Corresponding author. E-mail address: [email protected] (A. Braaksma)
place from the stipe towards the gill tissue during postharvest development (Braaksma et al., 1994), an inhibitory effect of stipe trimming upon cap opening might be possible. However, no effects on cultivar U1 are found in this respect; rather than increasing shelf-life, stipe trimming in U1 merely results in a larger decrease in dry weight in the cap tissue in favour of the gill tissue (unpublished observations). In a preliminary report, Beelman et al. (1993) reported positive effects of harvest time upon the quality and shelf-life of mushrooms, but did not provide supporting data. Our objective, therefore, was to see if there are beneficial effects of earlier harvest times upon postharvest development, with cap opening being a quality indicator.
0925-5214/99/$ - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 ( 9 9 ) 0 0 0 1 9 - 8
196
A. Braaksma et al. / Posthar6est Biology and Technology 16 (1999) 195–198
2. Materials and methods Mushrooms (Agaricus bisporus) strain U1 were grown in four rectangular plots of 1.5 ×1.4 m within a larger bed of 18 × 1.4 m used for the commercial production of mushrooms. The growing chamber contained 24 beds. The mushrooms were at the second flush stage since it is generally accepted that mushrooms from this stage are more stable in quality and yield. The harvest dates were determined by the grower for each crop, because of uncertainties associated with the use of spawn and variations in the compost and growth environment. Harvest dates are uncertain until 3–4 days before harvest when the first fruiting bodies appear. There were four collections at each commercial harvest from one marked rectangular plot: 2 days and 1 day before the planned harvest, the day of the commercial harvest, and finally 1 day after the commercial harvest. On the marked rectangles, no single mushroom was harvested before the indicated time. The mushrooms were transported to the laboratory within 1 h of each harvest and stored at 20°C with RH\ 90%. They were then sorted by cap diameter into eight categories: 15 – 20, 20 – 30, 30 – 40, 40–50, 50–60, 60 – 70, 70 – 80, and \ 80 mm, and stored at 20°C ( \ 90% RH) for 3 days. The percentage of mushrooms with either an intact velum, a broken velum or an open cap (broken veil and an opening that exceeds 1 mm) were determined every 24 h. The experiment was repeated twice, with an average of 3000 mushrooms involved in an experiment. Statistical analysis was carried out with Genstat 5.3.2 (1993). The three different stages of the mushroom’s cap (‘closed’, ‘broken’ and ‘open’) represent ordinal data and therefore the three different stages of the cap are not independent. Furthermore, they represent proportions of the total number of mushrooms harvested and we can therefore assume that they follow a multinomial distribution. McCullagh and Nelder (1989) (see pp. 178 – 182 for an example) specify a suitable generalised linear model (GLM) which would be suitable to describe the effect of the explanatory variables
cap diameter and harvest time on the state of the cap during postharvest storage. The data were tested for main effects and the interaction of the explanatory variables at the 5% significance level. As the experiment was performed three times, the repetition number was also included as an effect in the model to describe the differences between the repetitions. The model was not tested for significance of the repetition effect. For each of the four different storage periods after the harvest time, submodels were created that lacked one of the terms (either main or interactive). These submodels were then compared with the full model to assess the significance of the dropped term. The significance was tested using the comparison of the mean difference of deviation with a x 2 distributed random variable.
3. Results and discussion It is important for the relevance of this study to know if the parameter used in this study (cap diameter) is proportional to the weight of the entire mushroom (a commercially important parameter). The relationship between cap diameter and weight was determined for each experiment and it was found that the weight of the mushrooms closely correlated with the square of the diameter of the cap. The level of significance r 2 was always 99% or higher, except in one case where it was 98%. When fitted to a linear function, r 2 dropped to approximately 96%. The yield of a typical subharvest from the plots on the growing beds was 70 mushrooms m − 2 on the first harvest day with a total weight of 0.38 kg m − 2. On the second day the harvest was 226 mushrooms m − 2 with a total weight of 2.0 kg m − 2; on the third day, 401 mushrooms m − 2 with a total weight of 5.2 kg m − 2 and on the fourth day, 624 mushrooms m − 2 with a weight of 13.0 kg m − 2. The effect of harvest time and the influence of initial size at harvest upon cap opening during storage was statistically analysed for all sizeclasses at each harvest day (thus one experiment consisted of 32 data sets).
A. Braaksma et al. / Posthar6est Biology and Technology 16 (1999) 195–198
Neglecting the interaction between harvest time and initial cap diameter, a close examination of the collected data showed that a smaller cap diameter was associated with less cap opening during the 3 day storage period. The main trends of the effect of harvest time showed that the earlier the mushrooms were harvested, the less cap opening occurred during the three subsequent days of storage; the smallest mushrooms (cap diameter of 15–20 mm) showed no cap opening during a 3 day storage period, irrespective of the day of harvest. A comparison of the full model with a submodel lacking the interaction term between initial cap diameter and harvest time shows that this interaction was significant irrespective of the storage period. This implies that both explanatory
197
variables, initial cap diameter and harvest time, have a significant effect on the state of the mushroom’s cap during storage. Through the three repetitions of the experiment the effect of the diameter was present at a high level of significance and its effect depended on the harvest time and vice versa. The level of significance (r 2) was 99% or higher in all cases, except for one where it was 98%. These levels of significance were at 5% confidence limits and did not change when they were recalculated at 1% confidence limits. The effect of harvest time can be clearly seen in Fig. 1(a–c), where the results of a typical experiment are shown. In Fig. 1(a), for the size-class of mushrooms with a cap diameter of 20–30 mm at harvest, it is clear that irrespective of the day of harvest, all mushrooms in this class initially had
Fig. 1. Percentage cap opening of mushrooms as affected by time of harvest and days of storage. All mushrooms were stored at 20°C and RH\90%. The cap opening is represented as percentages of the total number of mushrooms involved. The total number for each harvest day is in Section 2. The data are derived from a typical experiment: first day of harvest, white square; second day of harvest, diagonal stripes; third day of harvest, horizontal stripes and fourth day of harvest, dotted square. (a) Initial cap diameter of 20– 30 mm; (b) initial cap diameter of 30–40 mm; (c) initial cap diameter of 40 – 50 mm.
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A. Braaksma et al. / Posthar6est Biology and Technology 16 (1999) 195–198
closed caps. Even after a subsequent four day storage period, \95% of the mushrooms harvested on the first harvest day showed no cap opening. This was in contrast to mushrooms sampled on the fourth day of harvest, which had no closed caps after 4 days of storage. The mushrooms harvested on the second and third days had intermediate responses to the storage treatment. Mushrooms within one size-class but harvested on different days, were completely similar in size and appearance at the time of harvest. The cap opening of the 30 – 40 mm mushroom sizeclass during postharvest storage is shown in Fig. 1(b). These mushrooms show similar trends to those of the 20–30 mm class, except that these larger mushrooms opened their caps earlier during storage. This was particularly apparent where smaller mushrooms reached the 100% open cap stage at day 4 (Fig. 1a), whereas for the larger mushrooms (size-class 30 – 40 mm) the 100% stage was reached at day 2 – 3 (Fig. 1b). A similar trend was found in mushrooms with a cap diameter of 40 – 50 mm at harvest (Fig. 1c); the percentages of opening reached on days 2 and 3 of storage were higher than in the 20 – 30 and 30 – 40 mm sizeclasses, even when the mushrooms from the 40 – 50 mm size-class were harvested early (second and third day of harvest). This trend is stronger amongst larger mushrooms (results not shown). In spite of the fact that there is no difference in initial appearance if a mushroom is harvested earlier or later, it can be concluded that, if harvested later, cap opening occurs in a larger proportion of the mushrooms and cap opening is completed earlier during subsequent storage. The total yield of the whole growth chamber was between 10 and 12 kg m − 2. This was achieved by pre-picking mushrooms with a cap diameter of 20 – 40 mm on days 1 and 2 combined with the yield of the commercial harvest at the third day
.
itself. When all mushrooms were picked on day 2, lower yields resulted. The worst yield was 4 kg m − 2 and the best was about 6 kg m − 2. Therefore, while pre-picking results in a higher quality with respect to cap opening, it is not advisable for commercial reasons, unless the price for improved quality is correspondingly higher. From these data it can also be seen that the effect of harvest time is not linear over the four subsequent days of storage. Between the second and the third harvest day especially, there seems to be a discontinuity. It is hypothized that this is mediated by a change in an unknown hormonal signal from the mycelium. Further research is necessary to see if endogenous levels of growth regulators are involved in cap opening.
Acknowledgements The authors thank the CNC, the Dutch Mushroom Growers Organisation, for their financial support and Dr J. Harbinson for critically reading the manuscript.
References Beelman, R.B., Miklus, M.B., Mau, J.-L., Ajlouni, S.O., Simons, S.S., 1993. Selected cultural and harvest practices to improve quality and shelf-life of Agaricus bisporus. In: Chang, S., Buswell, J.A., Chiu, S.-W. (Eds.), Mushroom Biology and Mushroom Products, Proceedings of the First International Conference on Mushroom Biology and Mushroom Products, The Chinese University Press of the Chinese University of Hong Kong, pp.177 – 184 (23 – 26 August 1993). Braaksma, A., De Vrije, T., Jongen, W.M.F., Woltering, E.W.J., 1994. Aging of the mushroom (Agaricus bisporus) under post-harvest conditions. Postharvest Biol. Technol. 4, 99 – 110. McCullagh, P., Nelder, J.A., 1989. Generalized Linear Models. Chapman and Hall, London.