Methods and techniques for storing horticultural products
The importance of using fruits for fresh consumption
Fresh fruit was undoubtedly the first food in human food at the beginning of its evolution. Fresh fruit from fruit trees has been and continues to be the only finished product of nature, which is consumed in the state in which it is found, without the involvement of other energy-consuming products or processes. Therefore, due to the balance and harmony between the physicochemical components, the fruit constitutes one of the ready-made foods of nature, which can be eaten fresh. Technological operations of preparation decrease the specific food value of fruits.
Fresh fruits are living organisms, in the tissues of which complex metabolic processes take place, and after harvesting, under the action of their own enzymes. Conservation technologies are intended to reduce the intensity of metabolic processes, in particular respiration and sweating, as well as the activity of pathogenic microorganisms that generate decomposition processes.
Fresh fruits are one of the indispensable components of man’s rational nutrition. The food value of fruits eaten fresh, is due to their chemical components easily accessible to the human body, to which is added a series of exciting taste, olfactory and visual, which make them enjoyed with pleasure at any time of the day or season.
Due to the complex chemical composition of the fruits, as well as the important role they have in nutrition, the food requirement must include for daily consumption in a proportion of 10-15% fruits, they can not be substituted by other foods. In addition, excessively perishable fruits (strawberries, currants, blackberries, raspberries) and very perishable (cherries, cherries, apricots, peaches, plums), are consumers ‘ favorite fruits, some of which are classified as “luxury fruits” (eg. strawberries). In addition to food value, fruits in these categories have therapeutic properties when eaten fresh.
Chemically, the fruits contain water and dry matter (organic substances and mineral substances). The content of fresh fruits in water varies by species, as follows: 74% in plums, 91.5% in peaches, 93% in strawberries.
Sugars form the main mass of dry matter components in fruits (about 90%). The most widespread are monosaccharides (glucose, fructose), disaccharides (sucrose) and polysaccharides (cellulose, starch and pectin). Fruit sugars, unlike simple ones, are assimilated in the human body very easily, entering directly into the blood circuit, without transformations that require energy consumption.
Cellulose contained in smaller or larger quantities in fruits consumed fresh, plays an important mechanical role in digestion for the human body, favoring the elimination of residues.
Mineral substances are found in the form of compounds of the main metals (Na, K, Ca, Fe), or salts of carbonic, hydrochloric, phosphoric acids, etc.the content in mineral salts varies from one fruit species to another and from one variety to another, but also by pedological conditions, climate and maintenance technologies applied to the respective crops. Used in small quantities by the human body, their role is essential in the secretion of various glands, while also serving as buffer substances in internal metabolism, especially in gastric juice.
The content of fruits in organic acids is directly related to the genetic character of varieties and species, but is dependent on the degree of ripening of fruits. Acids print the sour taste of fruits, and the ratios set in the content of sugary substance and acidity, build harmony of taste.
The acidity of some fruits is given by the presence of acids (malic, citric, tartaric, succinic), which are in the form of esters or salts. Most cultivated fruit species produce fruits containing predominantly citric acid (strawberries, currants, raspberries, peaches, apricots.
Along with mineral salts, acids play a special role in the secretion of some glands and have the advantage that they do not raise the acidity level of gastric juice, being generally weak, easily metabolized in other substances. (Gherghi.A. et al, 2001)
The nutritional value of fruits eaten fresh is also given by the important quantities that they synthesize. Vitamins are biocatalysts of vital processes, indispensable for life, their absence from human metabolism causes serious functional disorders. Impossibility of preservation in the body of vitamins, implies the need for a permanent intake in the daily food components. Of the vitamins absolutely necessary for the proper functioning of the body, most of them are found in fruits eaten fresh. The vitamin content of fresh fruits depends on the genetic characteristics of the fruit species and varieties under cultivation.
1.1. Keeping fruit fresh:
Fruit preservation is a set of technological operations carried out in order to maintain the quality of the fruit for fresh consumption, an allowable time interval, characteristic of each species and implicitly variety, in order to extend the duration of consumption.
Storage is the technological stage of keeping fresh fruits in an enclosed space after harvesting for a certain period of time.
The preservation of fresh fruits is their property to resist the processes of alteration for a certain period of time after harvest, with the maintenance of the parameters that constitute the quality, within the limits accepted by commercial standards, in all stages of the recovery circuit. It is a genetically transmitted biological appropriation, which is assessed after the time of maintaining the quality of the fresh product, from the moment of harvest and until there is a danger of compromising their value of use.
The conservation of fresh fruits differs from one fruit species to another, being influenced by the multiple and conjugated action of many factors: species, variety, chemical composition, climatic conditions of the vegetation period, applied agrotechnics, metabolic and microbiological processes that take place in horticultural products after harvest.
The allowable shelf life is the period of time during which the fruit maintains its quality of fresh consumption under certain environmental conditions.
Keeping fruit fresh can be:
– Temporary (short-term) storage, when the fruit by its nature has a high degree of perishability or the commercial destination of the products requires this technological measure.
– Prolonged (long-term) storage, the fruits are kept for a variable allowable time interval, determined according to the equipment of the storage space, the species and variety of fruits.
Perishability is the appropriation of fresh fruit to lose its use value, faster or slower, under the thermohydric conditions of the environment or inside a storage space in which they are found at a given time.
The perishability of horticultural products is a genetic appropriation and is determined by the physicochemical, morphological and physiological peculiarities that they have and are manifested both during growth and maturation, as well as during their storage and preservation (Jamba.A. et al, 2002).
According to the recommendations of the United Nations Economic Commission, from the point of view of perishability, fruits, as horticultural products, are divided into 4 groups with a similar degree of perishability: extremely perishable, very perishable, perishable and less perishable.
– Extremely perishable fruit. It is characterized by thin epidermis, intense breathing and a large area of contact with the environment. As a result of these peculiarities, the duration of maintaining their quality, even under optimal conditions of temperature and relative humidity of air, is 2-3 days. Under improper storage and conservation conditions, losses and downgrades of horticultural products exceed the limits permissible by law.
In the group of excessively perishable fruits fall: strawberries, blueberries, raspberries, blackberries, currants and gooseberries. These fresh products are subject to conservation and consumption of very short duration.
– Very perishable fruits. They have some peculiarities similar to the fruits of the previous group, in addition they are susceptible to mechanical damage, and the injured areas hardly heal or brown. The very perishable fruits are those of the drupaceae group: cherries, cherries, apricots, peaches, plums and nectarines.
Handling them is done with great care so as not to harm them during harvesting, transportation and storage. Under optimal conditions (relative air temperature and humidity), the shelf life is from 3-4 to 15-20 days.
– Perishable fruit. It is characterized by a biological activity of lower intensity after harvesting, compared to the fruits of the previous groups.
Harvesting at the optimum ripening time can lead to a shelf life under optimal conditions of temperature and relative humidity of air, up to 1-3 months for medium-ripening Apple and pear varieties.
– Less perishable fruits. This group includes fruits that are subject to long – term storage, for winter-spring consumption. These fruits have a resistant protective coating and heal well their mechanical injuries, and biological processes occur with low intensity if the optimal storage conditions, specific to each species and variety are respected.
The duration of storage depending on the species and variety varies from 3 to 8 months or even from one crop to another. In this group of fruits fall: apples and pears of late ripening.
1.2. Determining the optimal time of fruit harvesting
The definition of quality criteria for each species and Variety (without considering the factors determining the quality) is closely related to the degree of ripening of the fruit at Harvest. There is therefore a direct correlation between the value of the ripening indices at harvest and the fulfilment of the quality assessment criteria. Determining the optimal time of harvest is carried out using criteria, tests and indices. Simultaneous analysis of criteria, tests and indices shall be used to obtain the most accurate assessment.
The criteria for determining the degree of maturity and implicitly the optimal harvest time can be grouped as follows:
Sensory or organoleptic criteria, which include a series of indices of which are important: the color of the shell, the taste, the achievement of the characteristic fragrance of the fruit reached the maturity of consumption and the maximum individual mass. Sensory criteria are expedient, easy to appreciate and interpret. They are currently used in practice to determine the optimal time of harvest.
Analytical criteria require theoretical and practical knowledge of Biochemistry and Plant Physiology. Among these, we mention the following: the determination of soluble solids content on the way refractrometrică, the determination of the starch content, on the one hand, the determination of the firmness of the tissue, with the assistance of, the determination of the resistance to the detachment of the horticultural products of the plant; the determination of soluble carbohydrates-low acidity; the ratio of glucose-containing; the intensity of the respiratory and ethylene, endogenous, etc..
Phenological criteria determine the optimal time of harvest according to the number of days, the sum of the degrees of temperature and the number of hours of sunshine from flowering to harvest. The analytical and phenological criteria shall involve determinations and observations for each fruit species and variety, for a particular crop area, for a period of 3-10 years, with a view to establishing certain reference data and interpretations.
The choice of the optimal time of harvest depends on the following factors: the evolution of the fruits on the plants, the way of fruit recovery and the ripening capacity of the fruits.
Evolution of fruits on plants. The fruits of the fruit species, in general, can have value of use almost during the evolution on plants, from the growth phase to the harvest. The duration of fruit evolution on the plant depends on the species, variety, environmental factors and agrotechnical factors, and stretches for 5-6 weeks in strawberries and 5-7 months in autumn and winter apples and pears. During this time, the fruits go through 3 stages: growth, ripening, ripening and overripe.
The growth stage lasts from The Binding of fruits to harvesting. The growth of horticultural fruits is achieved initially by increasing the number of cells, following the process of cell division and then by increasing the size of fruit cells, a process that causes the volume of fruits to increase. At this stage, the process of deposition of reserve substances in fruits and in all plant organs is dominant. Low content in soluble carbohydrates (glucose, fructose and sucrose), high content in acids, tannins and protopectin, attribute to the fruits less pleasant sensory properties and reduced food value. At the stage of growth, horticultural products are odorless and with some exceptions all have an intense green color.
The fruit ripening stage lasts from the moment of changing the intense green background color to their ripening. First the intense green color of the fruit acquires light shades with a whitish or yellowish tinge, then the colors of the ripened fruit intensify, in parallel with the formation of aromas characteristic of the ripening phase.
Simultaneously with color changes, bio-chemical transformations take place that enrich sensory qualities. Acidity begins to gradually decrease by oxidation, salification and transformation of acids into other organic components, the content in tannins is greatly reduced by insolubilization and oxidation, starch begins to hydrolyze into simple carbohydrates, making the sweet taste appear, protopectin turns into pectin and pectic acids that make the pulp of horticultural products decrease its firmness. All these transformations improve the food value of the fruit.
The ripening (ripening) stage is a relatively short stage in the evolution of the fruit, at which time they meet the sensory properties characteristic of the ripe fruit. In this phase the taste of horticultural products becomes balanced, pleasant, as a result of favorable ratios between soluble carbohydrates, acids and tannins, and flavors and color reach the maximum content and intensity. The firmness of pulp tissues decreases greatly, which causes poor transport resistance of horticultural products. The ripening phase represents the optimal time for harvesting the fruits, which once they have been detached from the plant do not have the ability to evolve in ripening.
The stage of post-ripening or overcoating, is the final stage of the evolution of horticultural products in which the processes of deasimilation, deep degradation of chemical components and tissue decomposition predominate, all of which lead to qualitative impairments of sensory properties, a situation in which the fruits can no longer be eaten fresh. Acidity decreases to extinction, the color degrades becoming unattractive, the pulp softens excessively, the aromas disappear, the taste becomes unpleasant, anaerobic respiration is triggered with the transformation of sugars into acetic aldehyde, alcohols, ethers and other chemical components characteristic of the degradation process. The affected tissues Brown, the process taking place from the inside of the fruit pulp to the epidermis (Knee, 2001; 82 xxx).
Modu1 fruit recovery. Fruits as horticultural products, are used for fresh consumption and for conservation through industrial processing.
The choice of the optimal time of harvest for a particular destination of fruit production, is made at a certain stage of their evolution. There are some well-determined stages in the evolution of fruits, which are determined according to the time of consumption and the way of use, as follows:
A. The maturity of consumption, is the stage in which the fruits have reached the optimum specific to the variety and species with regard to taste, size, color and aroma, having at the same time adequate nutritional and energy value for consumption immediately after harvest.
B. Harvest maturity, is the stage in which fruit is harvested for long-distance transport or for preservation through storage for a long period of time.
The sensory properties of fruits at Harvest maturity are less expressed, but have a very good tissue firmness. For fruits intended for long-term conservation in fresh form, harvesting at this stage, is determined by climatic conditions that become unsuitable for further vegetation. Fruits of this category, reach maturity of consumption during the storage period.
C. Industrial maturity is the stage in which the fruits, by their physical, chemical and sensory properties correspond to a certain mode of conservation by industrial processes. They can be harvested at any of the stages of fruit evolution on the plant.
The ability to ripen, influences the choice of the optimal time of harvest. Depending on the ripening capacity, the fruits are grouped into two categories:
1. Fruits that are harvested at different times of the ripening phase, have the ability to mature, reaching the biochemical and organoleptic characteristics specific to the variety and species. They improve their sensory properties as a result of the continuation of biochemical transformations during long and short-term storage (apples and pears in autumn and winter), or long-distance transport for recovery (peaches).
2. Fruits that remain at the stage of evolution and maturation that they had at the time of Harvest, not having the ability to mature after being detached from the plants. The fruits of this category are harvested at full maturity to correspond from a sensory point of view to immediate consumption, while showing resistance to handling and transport.
For both product groups, harvesting at a stage other than the optimal time is correlated with incomplete fruit growth, insufficient nutrient accumulation and implicitly with quantitative harvest reductions, decreased storage capacity, fruit alteration, very poor transport resistance (Beceanu et al., 2003).
Factors that influence conservability and duration
A conservation technology achieves its purpose of preserving the qualitative qualities of the fruit for fresh consumption of the fruit, depending on a number of factors that influence the preservation and allowable duration of storage of the fresh fruit.
2.1. The influence of the species and variety of fruits on conservability
The species directly influences the conservation of fruits through its many genetic, physical and chemical properties. Nut fruits (nuts, hazelnuts, almonds) and seeds (apples, pears, quince) have good preservation. Within the framework of seed fruits, apples have better preservation than pears and quince. The fruits of the fruit species, of the group of pitted (cherries, cherries, apricots, plums, nectarines and peaches), and those of fruit bushes and strawberries have a low conservation. Horticultural products with good conservation are subject to long-term storage and storage for fresh consumption during the winter and spring periods.
Variety. Within the species, the varieties from which the products come the fresh fruit have different storage capacity. The variety factor is visible in all fruit species, which after the ripening age are divided into three groups: early ripening, medium ripening, late ripening. Late-ripening apples and pears, for example, retain a longer period of time and maintain their initial qualities well than autumn and summer ones.
2.2.Physical and thermophysical characteristics of fresh fruit
The physical and thermophysical properties of fruits with influence on their preservability are: size, shape, specific weight, volumetric weight, specific heat, tissue firmness, elasticity, thermal conductivity, electrical conductivity and energy value.
Size is the physical property of the fruit, which is expressed by caliber and mass. Frequently in the process of valorization it is used to visually appreciate the volume of fruits, valued as small, medium, large and very large. It does not have its own unit of measurement, it is assessed by the units of measurement of caliber (mm) and mass (g). In order to recover for fresh consumption, the sorted fruits are calibrated, separated by quality classes. This separation is made by gauges, by diameter and to a lesser extent by their length.
The mass of the fruit, is the individual weight of the fruit determined by weighing. It is a characteristic of species, variety and is influenced by pedoclimatic conditions, applied agrotechnics and specific gravity (density). Inside the species, the fruits of different varieties, at the same volume, have different weights, due to the variation of specific weight. Those with unit and superunit specific gravity always have a greater mass than those at which the specific gravity is subunit.
The Shape of the fruit, is a characteristic of species and Variety, also representing an indication of quality. It is determined by the shape index (I. F.) by the ratio of the height or length to the average of the two diameters measured in the equatorial area of the horticultural products.
Depending on the value of the shape index, 3 basic forms are found in horticultural products: spherical, flattened and elongated. The spherical shape is characteristic of products that have the index of the l-shape, that is, they have the height equal to the average of the two diameters, as in the case of some varieties of cherries, cherries, black currants, white currants, red currants and.a. flattened shape is characteristic of products in which the shape index has the subunit value ( < 1), i.e. the height is less than the average of the two diameters. The elongated shape is found in products where the shape index has a superunit value >1, sometimes their length or height is two to 8-10 times greater than the average diameter. The elongated shape is characteristic for the fruits of some varieties of apples, plums, strawberries.
Symmetry and surface condition are important elements that define the overall shape of horticultural products. Form, as a physical property is involved in the operations of sorting, calibration and packaging of fresh fruits.
The specific gravity (G. Sp), or density, is the ratio of the mass in the air (G) of the fruit to their volume (V), determined by placing in water at a temperature of 4°C, or in a standard solution. Water at a temperature of 4°C has a specific gravity = 1.
The specific weight of the fruits varies with the species and variety, being determined by the size of the air spaces, chemical composition, pedo-climatic conditions, applied agrotechnics and.A. has subunit, superunit or 1 values. Have superunit specific gravity (>l): cherries, cherries, plums, blackcurrants.
The proportion of chemical components directly influences the specific weight. Have high specific gravity, fruits in the chemical composition of which chemicals of high specific gravity predominate. The main chemical components in fruits have the following specific weights at room temperature: water = 1.0000 g/cm3, glucose = l,5600 g/cm3, fructose= l,6690 g/cm3, sucrose= 1.5880 g/cm3, cellulose= 1.2700 g/cm3 – l,6100 g/cm3, starch= 1.5010 g/cm3, malic acid= 1.6110 g/cm3, tartaric acid= 1.7590 g/cm3, citric acid= L,5420 g/cm3.
Pedoclimatic conditions, by their factors, influence the specific gravity. In years with precipitation in quantities greater than the normal average, the fruits increase in volume, having a specific gravity less than the normal average value.
From a technological point of view, the specific weight positively influences the volumetric weight, the resistance to transport, handling, packaging and keeping the fruit fresh.
Thermal conductivity is the property of heat transmission through the mass of horticultural products at temperature variation. Expressed in W / ml / h / K or Kcal/ml/H/oC.
Fresh fruits, like all horticultural products, tend to reach the temperature of the storage environment by heat exchange (yield and absorption). The change in the temperature of fresh fruit in the storage space is influenced by the water content, the volume of products, and the amount of air in the tissues.
Fruits with a high water content and a low volume of intercellular spaces, have a higher thermal conductivity, compared to fruits that have a lower water content and have a higher volume of intercellular spaces. Fruits are valued as heat-conducting evils, as they slowly heat up and cool down. On this physical property is based pre-cooling, preservation by refrigeration. The lower the thermal conductivity, the harder the horticultural products heat up, breathing and sweating slow down and maintain their original quality for a longer time.