Role of the Waxy Skin Layer in Moisture Loss during Dehydration of Prunes

Abstract

Permeability studies of water through the skin and flesh of d'Agen plums have been carried out by radiotracer and PGSE NMR techniques as a function of moisture content. The results have shown that the diffusion coefficient of water through the skin layer increases as the fruit is dried at 70 degrees C or above. By contrast, the water diffusion through the fruit becomes more hindered as moisture is lost and structural collapse of the cell layers takes place. Values for diffusion coefficients of water at 21 degrees C through the fruit of 1 x 10(-)(9) m(2) s(-)(1) for fresh plums and 2.0 x 10(-)(10) m(2) s(-)(1) for fruit dried to 50% moisture content (wet basis) were found. Structural studies using scanning electron microscopy techniques were also performed. These showed that drying induces marked changes to the waxy skin layer of the fruit as well as the fruit flesh. These results are discussed in terms of the important role that the plum skin has in modulating the moisture loss process during dehydration, particularly at early stages of drying.

Selection of chemical and thermal pretreatment combination for plum drying at low and moderate drying air temperatures

“…Another reason causing this observation may be the fact that the phase change of the waxy layers of plums occurs only in the greenhouse in which drying air temperature reached up to 54.74°C. However, it takes much longer time compared to the time (2 h) at 60°C (Price et al, 2000) while it never starts under open atmosphere. Since the three-factor interaction was not statistically significant at the 24 h of drying, significant two-factor interactions were examined in detail.…”

“…Another moderately effective pretreatment combination consisted of dipping the samples into 60°C hot water (coded as T8). Price et al (2000) reported the quick phase change of the cuticular waxes of plums from the crystalline form to the amorphous phase at high drying temperatures (P70°C). This phase change resulted in increase of water permeability of plum skin.…”

“…Moisture permeabilities of the skin and flesh of d'Agen plums depended on the temperature of drying air and moisture content of plums (Price, Sabarez, Storey, & Back, 2000). Drying plums at high temperatures (P70°C) does not need pretreatments while drying at lower temperatures (40-60°C) requires pretreatment process (Price et al, 2000).…”

“…Moisture permeabilities of the skin and flesh of d'Agen plums depended on the temperature of drying air and moisture content of plums (Price, Sabarez, Storey, & Back, 2000). Drying plums at high temperatures (P70°C) does not need pretreatments while drying at lower temperatures (40-60°C) requires pretreatment process (Price et al, 2000). The moisture diffusivity of the waxy skins of fresh fruits can be improved by chemical pretreatment (Doymaz, 2004;Doymaz & Pala, 2002Pangavhane, Sawhney, Pointing & McBean, 1970) or by physical pretreatments (Cinquanta, Di Matteo, & Esti, 2002;Di Matteo, Cinquanta, Galiero, & Crescitelli, 2000.…”

Efecto de la composición de recubrimientos comestibles a base de hidroxipropilmetilcelulosa y cera de abeja en la calidad de ciruelas, naranjas y mandarinas.

“…Pérdida de peso La pérdida de agua por transpiración del fruto es la principal causa de pérdida de peso del mismo durante el almacenamiento. En ciruelas esta deshidratación se ve reducida por las presencia de una cobertura cérea externa o cera epicuticular (Mrozek y Burhardt, 1973;Storey y Price, 1999) que aumenta la resistencia de la cutícula a la difusión de agua (Price et al, 2000). La aplicación de recubrimientos hidrofóbicos en la superficie de las frutas aporta una barrera adicional a la deshidratación .…”