Effect of processing on the texture and sensory attributes of raspberry (cv. Heritage) and blackberry (cv. Thornfree)
Introduction
Texture is one of the organoleptic quality attributes appreciated by the consumer of fruits, and the major contributor to the texture of fresh fruits is cell turgor pressure. Many studies have focused on turgor pressure (Alvarez et al., 2000, Brusewitz et al., 1989, Lin and Pitt, 1986, Ramana and Taylor, 1994) as the factor that preponderantly controls the stiffness of liquid-filled cells. Turgidity is in fact the characteristic largely responsible for the final degree of firmness in cherries (Alonso, Canet, & Rodríguez, 1994). In delicately textured fruits, freezing causes a loss of turgidity and firmness (Alonso, Rodríguez, & Canet, 1995). During freezing, ice begins to form in the extra-cellular medium and progresses via the cytoplasm when the cell membrane loses permeability (Alonso, Canet, & Rodríguez, 1997). Decompartmentalization caused by ice crystals prevents the return of water to the intracellular medium during thawing, causing loss of turgidity and hence of fruit texture (Grout et al., 1989, Reid, 1993). The freezing rate determines the size of ice crystals that form, and this in turn determines the degree of structural damage, which produces a change in the rheological parameters of the tissue (Alvarez & Canet, 1997). A number of authors have noted that fast freezing rates positively affect the texture of fruits, including cherries (Alonso et al., 1994), blueberries and blackberries (Martí & Aguilera, 1991), raspberries (Crivelli and Senesi, 1990, Reynoso and Michelis, 1994) and strawberries (Delgado & Rubiolo, 2005).
Also, in order to enhance fruit and vegetable firmness and attenuate any freezing-induced loss of texture, thermal or calcium pre-treatments (Alonso et al., 1995, Canet and Hill, 1987, Fuchigami et al., 1995) have been proposed that preserve firmness. The effect of calcium on vegetable texture has been attributed to the formation of calcium bridges between galacturonic acid residues. McFeeters and Armstrong (1984) suggested that the textural effects of calcium were a result of calcium binding at sites other than pectic carboxyl groups. Application of calcium treatments increased firmness and pectinesterase activity in frozen sweet cherries (Alonso, Canet, & Rodríguez, 1993). In calcium-treated cherries, a decrease in the degree of pectin esterification has been reported, and an increase in both the EDTA-soluble pectin fraction and the Ca2+ cation content in the cell wall (Alonso et al., 1995). The calcium–pectin complex formed acts as an intracellular cement to give firmness to vegetable tissues. Independent of the formation of Ca-pectates, the degree of esterification has been shown to play an important role in the rigidity and configuration of pectic substances whereby the stiffness of the pectic macromolecule increases with increasing methoxyl content (Hudson & Buescher, 1986). Thus, firm tissue seems to be associated with the formation of insoluble and methylated pectic substances. Addition of low methoxyl pectin was undertaken to test the hypothesis that increasing the degree of esterification of pectic substances may facilitate formation of divalent bridges between residues of galacturonic acid attached to adjacent pectic chains in presence of Ca2+ cations.
The term “firmness of fruit” is commonly used to describe a parameter assessed by means of empirical mechanical tests and understood as an attribute that ought to be maintained during storage and processing (Alvarez, Canet, & Tortosa, 1997). Firmness, interpreted as a mechanical response intrinsic to the fruit structure, is influenced by the stage of physiological development, degree of ripeness, damage and identification, fibrousness and turgidity (Alonso et al., 1994). A variety of methods have been used to evaluate these characteristics, and various interpretations have been made of mechanical parameters. Santerre, Cash, and Iezzoni (1991) designed a multiple stoning cell (five units) for use on texturometers. Comparing these results with the results from a test using the Kramer Shear Cell, they concluded that a multiple test was required to assess the texture of cherries.
The objectives of the current study were: (1) to determine the effect of the pre-treatment with calcium, low methyl pectin and combined solutions on the texture of fresh raspberries and blackberries; (2) to investigate the effect of freezing and thawing rates on the texture and sensory attributes of both fruits and to find the best conditions for each one; (3) to determine the effect of the pre-treatment with calcium, low methyl pectin and combined solutions on the texture and sensory attributes of frozen/thawed raspberries and blackberries; and (4) to find the mechanical parameters that best express the firmness of both fresh and frozen fruits.
Section snippets
Plant material
Raspberry fruits (Rubus idaeus L. cv. Heritage) and blackberry fruits (Rubus fruticosus L. cv. Thornfree) were obtained from commercial orchards in the region of Cova da Beira (Covilhã, Portugal), and harvested at the commercial maturity stage. Both fruits were collected manually and brought to the Estação Agronómica Nacional (Oeiras) within 12 h after harvest via refrigerated transport. On arrival, fruits were stored in a chamber at 2 °C and 90% relative humidity and were kept there for a
Effect of protective pre-treatments
Table 2 shows average values of the different texture parameters in the calcium pre-treatment at the concentrations chosen for each fruit. In the case of raspberry, the pre-treatment significantly affected the values of KSC, back extrusion and multiple penetration maximum forces (FKSC, FE, FMP), and of compression and multiple penetration slopes (SC, SMP) (P ⩽ 0.01). The texture parameter values were highest in the samples treated with 100 mM of CaCl2, which with the exception of the back
Conclusions
A pre-treatment with CaCl2 (100 mM), applied independently or combined with LMP, should be applied in raspberry and blackberry fruits in order to prevent loss of firmness induced by freezing and thawing processes. Objective texture parameters evidenced as blackberry fruit was more susceptible than raspberry fruit to the effect of pre-treatments. Multiple penetration maximum force (FMP) may be the most suitable parameter for assessing the firmness of both fresh and pre-treated fruits without
Acknowledgements
The authors wish to thank the Instituto Nacional de Investigação Agrária (INIA Proj Piddac 117/97), the Consejo Superior Investigaciones Científicas (CICyT, Project ALI98-1055) (Spain) and Junta Nacional de Investigacão Científica y Tecnológica de Portugal (Proc. no. 423/CSIC), which financially supported this cooperative research.
References (34)
- et al.
Microstructural changes in strawberry after freezing and thawing processes
Lebensmittel-Wissenschaft und-Technologie
(2005) - et al.
Measurement of pectin methylation in plant cell walls
Analytical Biochemistry
(1984) The effects of freezing and thawing on food quality
- et al.
Parameters affecting freezing storage and transport of individually frozen Schoeneman raspberries
Revue Internationale du Froid
(1994) - et al.
Effect of various thermal pre-treatment on the texture of frozen cherries (Prunus avium L.) Related enzyme activities
Zeitschrift für Lebensmittel Untersuchung und Forschung A
(1993) - et al.
Mechanical assessment of texture of sweet cherries: effects of freezing
Journal of the Science of Food and Agriculture
(1994) - et al.
Thermal and calcium pretreatment affects texture, pectinesterase and pectic substances of frozen sweet cherries
Journal of Food Science
(1997) - et al.
Effect of calcium pretreatments on the texture of frozen cherries. Role of pectinesterase in the changes in the pectic materials
Journal of Agricultural and Food Chemistry
(1995) - et al.
Effect of pre-cooling and freezing rate on mechanical strength of potato tissues (cv Monalisa) at freezing temperatures
Zeitschrift für Lebensmittel Untersuchung und Forschung A
(1997) - et al.
Rheological characterization of fresh and cooked potato tissues (cv Monalisa)
Zeitschrift für Lebensmittel-Untersuchung und-Forschung A
(1998)
Effect of freezing rate and programmed freezing on rheological parameters and tissue structure of potato (cv Monalisa)
Zeitschrift für Lebensmittel-Untersuchung und-Forschung A
Effect of turgor pressure on the cutting energy of stored potato tissue
European Food Research and Technology
Effect of temperature on firmness of fruits and vegetables
Journal of Food Science
Microbiological aspects of frozen foods
Effects of storage time and static preloading on the rheology of potato tissue
Journal of Texture Studies
Determination of the moisture content of some fruits and vegetables by microwave heating
Journal of Microwave Power and Electromagnetic Energy
A comparison of several blanching methods on the texture and ascorbic acid content of frozen potatoes
International Journal of Food Science
Cited by (44)
Inactivation of hepatitis A virus and norovirus on berries by broad-spectrum pulsed light
2022, International Journal of Food MicrobiologyFreezing of fresh Barhi dates for quality preservation during frozen storage
2018, Saudi Journal of Biological SciencesCitation Excerpt :Higher values of hardness, chewiness and resilience of the pulp indicate better quality products (Zhang et al., 2007; Krause et al., 2008; Kaushik et al., 2013). Several researchers have studied the effects of freezing on textural quality of fruits (Delgado and Rubiolo, 2005; Buggenhout et al., 2006; Sousa et al., 2007). Enzymatic activity is responsible for the quality deterioration in most of the frozen fruits.
Cryogenic freezing of fresh date fruits for quality preservation during frozen storage
2018, Journal of the Saudi Society of Agricultural SciencesCitation Excerpt :This is probably due to decrease in the injurious effects of crystallization and recrystallization on the microstructure of fruits tissues during such quick freezing method. These results proved the reported significant role of the freezing rate in maintaining the texture of frozen foods (Van Buggenhout et al., 2006; Delgado and Rubiolo, 2005; Sanz et al., 1999; Sousa et al., 2007; Sun and Li, 2003; Zhang et al., 2004). Invertase enzyme activity was not detected in Brahi fruits (Khalal stage).
Pre-harvest sprays of hexanal formulation for extending retention and shelf-life of mango (Mangifera indica L.) fruits
2016, Scientia HorticulturaeCitation Excerpt :The pre-harvest sprays of hexanal formulation helped the fruit retain its firmness during storage conditions. The firmness of the fruit is commonly defined as a mechanical response essential to the fruit structure which is influenced by the physiological development, degree of ripeness, damage and turgidity and it is an attribute which has to be maintained during post-harvest handling, transport, storage and processing (Sousa et al., 2007). Martinez-Romero et al. (2006) reported that there was a linear correlation between turgor pressure and firmness in sweet cherries.
Physical and mechanical properties of raspberries subjected to osmotic dehydration and further dehydration by air- and freeze-drying
2016, Food and Bioproducts ProcessingTrends in maintaining postharvest freshness and quality of Rubus berries
2023, Comprehensive Reviews in Food Science and Food Safety