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Microstructural analysis of fresh-cut red bell pepper ( Capsicum annuum L.) PowerPoint PPT Presentation


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Procedure I 0 d. Procedure I 7 d. Procedure II 0 d. Procedure II 7 d. Procedure III 0 d. Procedure III 7 d. Microstructural analysis of fresh-cut red bell pepper ( Capsicum annuum L.) aiming at postharvest quality optimization. Susana C. FONSECA * Cristina L. SILVA

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Microstructural analysis of fresh-cut red bell pepper ( Capsicum annuum L.)

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Microstructural analysis of fresh cut red bell pepper capsicum annuum l

Procedure I

0 d

Procedure I

7 d

Procedure II

0 d

Procedure II

7 d

Procedure III

0 d

Procedure III

7 d

Microstructural analysis of fresh-cut

red bell pepper (Capsicum annuum L.)

aiming at postharvest quality optimization

Susana C.FONSECA *

Cristina L. SILVA

F. Xavier MALCATA

Introduction

  • Rationalization of deterioration processes that take place during postharvest of fresh fruits and vegetables, and in particular fresh-cut ones, is essential to optimize postharvest quality and maximize shelf-life.

  • This requires understanding microstructure, and relating it to macroscopic quality characteristics of the food product.

  • Scarce work has indeed focused to date on the microstructure of fresh and fresh-cut fruits and vegetables.

  • Scanning electron microscopy (SEM) is an interesting technique for microstructural studies.

Scanning electron micrographs of fresh-cut red bell pepper, according to different preparation procedures and storage time:

Objective

Application of SEM to evaluate microstructure of fresh-cut red bell pepper, after cutting and maintaining (for 0, 4 and 7 d) under refrigerated storage. In order to achieve such a goal, two sub-objectives were addressed: i) to optimise the sample preparation procedure prior to analysis of red bell pepper by SEM, and ii) to develop an adequate methodology to quantify SEM images.

Materials & Methods

Fresh red

bell peppers

Wash and dry

Core removal

Cut in dices

Storage (2 ± 0.5 C

and 90-95% RH

Product

preparation

after 0, 4 and 7 d

Procedure I

Procedure II

Procedure III

* Cellular destruction

rating scale:

1 = absence

3 = very little

5 = moderately,

7 = very much

9 = extreme

frozen

1 d at -80 °C

frozen by

immersion in N2

frozen by

immersion in N2

Microstructural

analysis

freeze-dried

freeze-dried

stored at -80 °C

stored at -80 °C

stored at -80 °C

Observation by low vacuum SEM

Image

analysis

Delivery by e-mail

to panellists

Preparation of electronic

evaluation sheet

Image selection

Panellists asked to

rate each image*

Results

  • Apparent differences were observed between preparation procedures; in Procedure III, a dendritic structure appeared during ice microcrystal formation inside the cells.

  • Differences in microstructural effects associated with time of storage after cutting were also observed; samples cut and stored for 7 d showed a great degree of cell decompartmentation and collapse, reflected by poor definition of cell walls — as compared with samples taken just after cutting.

  • Statistical analysis of experimental data generated by the panel pertaining to SEM images indicated that there are microstructural differences between pepper samples from the distinct preparation procedures (p=0.001) and time after cutting under refrigerated storage (p=0.001); however, the interaction between these two factors was not statistically significant (p=0.051). Frozen samples presented higher cellular destruction than via the other two procedures, and no statistical significant differences were observed between these two. Red bell pepper samples stored for 4 and 7 d presented (as expected) higher degree of cellular destruction than their initial sample counterpart.

9

8

7

6

Degree of cellular destruction

5

4

3

2

1

0

1

2

3

4

5

6

7

Time, d

Degree of cellular destruction of red bell pepper over time under refrigerated storage (average±standard deviation), according to different preparation procedures:

(●) procedure I; (■) procedure II; and (▲) procedure III.

Conclusions

  • SEM was successfully applied in the microstructural study of fresh-cut red bell pepper; it provided a clear viewing of microstructural changes over time after cutting, under refrigerated storage. Red bell pepper samples stored for 4 and 7 d presented (as expected) higher degree of cellular destruction than samples at 0 d. Samples for SEM prepared via freeze-drying produced better quality images than frozen samples.

  • The methodology applied, which was based on panel evaluation of SEM images, proved a valuable tool to obtain quantitative parameters.

  • This work allowed optimization of preparation procedures of sample, and development of successful methodology for quantitative image analysis – which will eventually permit application to related work in other food matrices.

Author S. C. Fonseca acknowledges financial support by FCT (Portugal), via a PostDoc fellowship (BPD/1601/2000). The authors acknowledge financial support through Programa Operacional para a Agricultura e o Desenvolvimento Rural – Project AGRO nº 822 (Novas Tecnologias de Processamento de Hortofrutícolas Congelados – EMERCON).

Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Dr. António Bernardino de Almeida, P-4200-072 Porto, Portugal

* E-mail: [email protected]


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