CHERRY QUALITY CONTROL: Machine based:
We describe an artificial vision system for the quality control of cherries. We develop image-processing software determining three types of information describing the quality of the fruit: the color as an indicator of ripeness, the presence of defects such as cracking, and the size. The sorting of cherries conditioned by all these criteria is carried out at a high cadence (20 cherries/s). Real-time image processing is then necessary. A simple sensor is used to synchronize the processing and the sorting of cherries. Air actuators are used to eject them after quality control by vision. We present the architecture of the developed system. We show its efficiency through experimental results and we give some perspectives of improvement.
CHERRY, PRUNUS AVIUM / ROSACEAE QUALITY
Postharvest Atmosphere Management
After the harvesting it is recommended to transport the cherries in freezer lorries. If this is not possible, we must take into account that they must be put in cold rooms within the 4 hours that follow the harvesting, considering that they must not be subject to high temperatures during the transport. The processes causing quality loss are three times faster at 20ºC than at 10ºC. At any rate, it is necessary to reduce as much as possible the time between the harvesting and the arrival at the cold storage room.
During the transport and storage takes place the ‘respiration’ of the fruit. It is very important to keep them at low temperatures so that the rate of respiration of the fruit and the subsequent heat emission is the minimum. When emitting heat, the temperature increases, so the foodstuffs decompose rapidly.
The temperature at which the cherries must be put under depends on their immediate use; if the fruit is intended for immediate consumption, it will not require the same treatment for keeping quality. If the cherries are sold the day after their harvest, they should be stored in cold rooms at 8-12ºC. However, if they have to be kept for more than 8 days after their harvesting, they must be stored in cold storage rooms at 0ºC to assure their arriving to the consumer in perfect condition.
Days from harvesting to marketing::Optimal temperature (ºC)
Source: Cherries: WEBSTER A.D. & N.E. LOONEY (1996). Crop Physiology Production and Uses.
When the cherries arrive from the field they are usually cooled with different methods before they start preparing them, this is what we call precooling. For this purpose they use water or air at low temperatures.
Relative humidity, the water content in the air, is due to be taken into account for preserving the cherries. Cherries have high quantities of water; if the environment is extremely dry the fruit has a tendency to loose water and to dry, and that is why this parameter should be controlled. Therefore, we must keep relative humidity as high as possible, so the cherry looses the lesser quantity of water possible.
Once we have removed the leaves and the cherries that satisfy the minimum requirements, they are subject to a second precooling before they are packaged. Immediately afterwards they are taken to the cold rooms where they will be kept until they are sold.
Inside these rooms there is a modified atmosphere that diminishes the deterioration of the fruit. The temperature is usually around 0ºC. The fruit is put in polyethylene bags, a kind of plastic where the oxygen levels are between 3-10% and carbon dioxide at 10-15%. All these procedures allow to keep the harvest without losing its properties from 6 to 10 weeks. It is possible to maintain the cherries in perfect condition for a time, but, with no doubt, cherries are not adapted to be stored for long periods of time.
If the keeping quality processes are not carried out properly or if the produce is not packaged correctly, there may appear some diseases that could spoil the fruit in short time.
Cherries may show various physiological alterations or diseases during their storage and conservation.
- Brown rot: Caused by a pair of fungi called Monila fructicola and Monila laxa3; the symptoms are brown or black spots that spread rapidly all over the fruit. On the damaged tissue there grows some short hairs.
- Gray mould (Botrytis cinerea): It is possibly the worse disease of the harvested cherries. The infection takes place in the field and later on it is developed in the storage rooms. At the beginning it is a brown spot, afterwards the fruit meat turns watery and the spot acquires a darker colouring.
- Blue rot: Caused by the fungus Penicillium expansum, it normally gets in the fruit through a damaged part of the skin. The first symptom is a light brown spot, then the damaged tissue seems to be soft and watery, later on the skin tears off and there appear white spots of mould.
- Ryzopus spp. rotting: The infection takes place in the same way as the blue rot; this fungus does not develop below 8ºC. It shows white fibers that will develop spore heads.
- Alternaria (Alternaria spp): It has the form of a spot in the skin with olive coloured spores and white fibers. The damaged tissue is later on teared off from the meat that surrounds it.
- Fungus Cladosporium herbarium: When the tissue deteriorates it turns dry and hard and the colour changes from gray to black. Usually, this fungus infects the fruit through the injuries of the skin.
Quality and food safety is fundamental to us at Koala Cherries.
We have in place a rigorous and continuously improving Food safety and Quality system, based on current SQF and customer quality codes. We are independently audited to these codes annually. We monitor the quality of the fruit on the trees; again on arrival at the packing shed; throughout the fruit packing process, all the way to dispatch…and even beyond. We monitor natural sugar levels, temperature and fruit quality so that our customers will receive consistently beautiful fruit.
Factors Affecting Quality and Health Promoting Compounds during Growth and Postharvest Life of Sweet Cherry (Prunus avium L.)
Sofia Correia1*, Rob Schouten2, Ana P. Silva1 and Berta Gonçalves1
1Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal
2Horticulture and Product Physiology, Wageningen University, Wageningen, Netherlands
Sweet cherries are attractive fruits due to their taste, color, nutritional value, and beneficial health effects. Sweet cherry is a highly perishable fruit and all quality attributes and the level of health promoting compounds are affected by growth conditions, picking, packing, transport, and storage. During production, the correct combination of scion × rootstock will produce fruits with higher firmness, weight, sugars, vitamins, and phenolic compounds that boost the fruit antioxidant activity. Orchard management, such as applying drip irrigation and summer pruning, will increase fruit sugar levels and total phenolic content, while application of growth regulators can result in improved storability, increased red coloring, increased fruit size, and reduced cracking. Salicylic acid, oxalic acid, acetylsalicylic acid, and methyl salicylate are promising growth regulators as they also increase total phenolics, anthocyanins, and induce higher activity of antioxidant enzymes. These growth regulators are now also applied as fruit coatings that improve shelf-life with higher antioxidant enzyme activities and total phenolics. Optimizing storage and transport conditions, such as hydro cooling with added CaCl2, chain temperature and relative humidity control, are crucial for slowing down decay of quality attributes and increasing the antioxidant capacity. Application of controlled atmosphere during storage is successful in delaying quality attributes, but lowers ascorbic acid levels. The combination of low temperature storage in combination with modified atmosphere packaging (MAP) is successful in reducing the incidence of fruit decay, while preserving taste attributes and stem color with a higher antioxidant capacity. A new trend in MAP is the use of biodegradable films such as micro-perforated polylactic acid film that combine significant retention of quality attributes, high consumer acceptability, and a reduced environmental footprint. Another trend is to replace MAP with fruit edible coatings. Edible coatings, such as various lipid composite coatings, have advantages in retaining quality attributes and increasing the antioxidant activity (chitosan) and are regarded as approved food additives, although studies regarding consumer acceptance are needed. The recent publication of the sweet cherry genome will likely increase the identification of more candidate genes involved in growing and maintaining health related compounds and quality attributes.
Sweet cherry (Prunus avium L.) is one of the most popular table fruits. In 2014, the estimation of the world total cherry production was 2.294 thousand metric tons, with the top three producing countries (Turkey, USA, and Iran) producing 43% (FAO, 2017). Sweet cherry is greatly valued by consumers due to its taste, color, nutritional value, and beneficial health effects. Important quality characteristics of cherry fruits are weight, color, firmness, sweetness, sourness, flavor, and aroma (Crisosto et al., 2006). Sweet cherry is a highly perishable fruit containing significant levels of important nutrients such as potassium, dietary fiber, ascorbic acid, carotenoids, anthocyanins, and phenolic acids with only low caloric content (USDA, 2017). The objective of this review is to provide understanding of the cherry pre-and postharvest changes, and packaging technologies with regard to critical quality indicators and health benefits, thereby updating previous reviews by Predieri et al. (2003), Romano et al. (2006), McCune et al. (2010), and Wani et al. (2014). It also provides a peek on the road forwards with regard to the availability of new technologies. Part of these technologies are related to improving the circumstances in the chain as to gain access to long distance markets. Examples of these are the use of natural compounds and biodegradable films for modified atmosphere packaging (MAP) and edible coatings. The other part is related to improving the properties of the sweet cherry fruit itself; these are presented by showing the recent advances in marker assisted breeding preservation.
Sweet Cherry Quality Factors
Fruit maturity is one of the key factors determining overall fruit quality. Cherries should be harvested at the end of the maturation stage when they are fully ripe to ensure a good eating quality (Serrano et al., 2009). Although, the harvest timing varies based on the sweet cherry cultivars, there is harvest window of <5 days for harvesting fruit of optimal quality. The harvest season for sweet cherries is short and labor intensive. Ripe fruit are prone to mechanical damage and cooling directly after harvest is important (Dever et al., 1996; Chauvin et al., 2009).
During early developmental stages, skin color changes, and softening starts, glucose, and fructose accumulate, together with a rapid increase in fruit size. In later development stages, ascorbic acid and anthocyanin accumulate, antioxidant activity increases, and fruit flesh darkens (Serrano et al., 2005). A significant increase of total phenols was obtained in “Pico Negro” cherries during ripening and consequently, an increase in antioxidant activity, which may have beneficial health effects (Serradilla et al., 2012). Early-harvested cherries suffered from low acceptance due to the low sweetness while late-harvested cherries showed low acceptance due to low texture (Chauvin et al., 2009). Nevertheless, higher sensory scores were obtained for late-harvested sweet cherry fruits, especially for skin color and flavor intensity (Chauvin et al., 2009; Serradilla et al., 2012). Harvested cherries show weight loss, changes in the sugar-acid balance, color, softening, and stem browning (Kappel et al., 2002; Bernalte et al., 2003; Alique et al., 2005). During postharvest storage (4 days at 20°C) “Ambrunés” fruits showed a decrease in sugar levels, skin color, firmness, and TA, whereas SSC remained fairly stable, decreasing from 15.2 to 14.8°Brix. Malic acid levels decreased up to 20%, which may indicate that malic acid is an essential substrate for respiration in cherries (Alique et al., 2005).
Assessment of the optimal maturity in the orchard is not straightforward due to the variation in maturity within a tree, but especially within an orchard. Orchard mapping can support growers finding the correct harvest window by sampling°Brix and firmness during growth, just as now is being applied for dry matter assessment per plot for mango (Subedi et al., 2013). This type of quality mapping (Zude-Sasse et al., 2016) may be helpful to scheduling future cherry harvest campaigns.
Color, Firmness, and Water Loss
Cherry fruit quality traits related to consumer purchase decisions are based on external quality attributes such as color, fruit size, stem freshness, absence of defects, and stem length (Predieri et al., 2004). Aroma, flavor, sourness, sweetness, and texture are also essential attributes (Romano et al., 2006; Díaz-Mula et al., 2009). Fruit color is, however, the main quality trait (Mozetič et al., 2004). Color development has been studied as function of cultivar, ripeness stage, and storage conditions (Esti et al., 2002; Gonçalves et al., 2007; Pérez-Sánchez et al., 2010). Large variation exists amongst sweet cherry cultivars grown in Italy with the skin color variation classified as dark—(e.g., “Black Star” and “Moreau”) and light type cultivars (e.g., “Gabbaladri” and “Napoleona Verifica”; Ballistreri et al., 2013). Dark red blush cultivars have a higher consumer preference when comparing with full bright red cherries (Pérez-Sánchez et al., 2010). Color change during maturation is mostly due to an increase in anthocyanin content, specifically, cyanidin-3-O-rutinoside and cyanidin-3-O-glucoside (Mozetič et al., 2004; Gonçalves et al., 2007; Serrano et al., 2009). Transcriptomic studies in cherry fruit maturation have been carried out to elucidate the role of abscisic acid (ABA) and ethylene (Ren et al., 2011) and ripening (Luo et al., 2014). PacNCED1 transcription induced ABA synthesis and accumulates during cherry ripening, which should play a crucial factor in regulation on the sweet cherry fruit ripening (Ren et al., 2011; Luo et al., 2014). The ethylene production via regulation of PacACO1 expression (1-aminocyclopropane-1-carboxylic acid oxidase) might be stimulated with exogenous ABA, which indicates that the ethylene is synthesized by cherries (Ren et al., 2011) to start anthocyanin biosynthesis (Luo et al., 2014).
Positive effects of light on biosynthesis of phenolic compounds, mainly flavonoids are reviewed by Zoratti et al. (2014). Extensive studies have been carried out on the effect of supplemental UV-light treatments to improve anthocyanin levels in sweet cherry skin (Arakawa, 1993; Kataoka et al., 1996). Moreover, the application of UV-C light in postharvest has also been mentioned as a promise tool for extension of fruit shelf life, by delaying fruit senescence, increasing flavonoid content, and antioxidant activity in fruits (Wang et al., 2009; Crupi et al., 2013; Rivera-Pastrana et al., 2013; Li, 2014). The application of blue light emitting diodes (LEDs) to increase anthocyanin levels in cherries could be a reality soon (Arakawa et al., 2017), increasing both color and health promoting potential.
In general, consumers prefer cherries fully ripe based on their dark skin color (Crisosto et al., 2003). However, consumers chose partially ripe over full ripe “Sweetheart” cherries (Chauvin et al., 2009) which indicates the importance of a number of less well understood attribute interactions in consumer acceptance. In general, the chromatic values at harvest are lower at full ripeness stage than at the partially ripe stage. During postharvest storage, a further reduction in lightness (L*) and hue angle (h°) values were observed which indicates that the cherries became darker (Gonçalves et al., 2007). Firmness is related to storability, providing resistance to fruit deterioration and mechanical injury (Esti et al., 2002). Late season cultivars are frequently firmer than early season cultivars (Usenik et al., 2005). Fruit firmness at harvest varies greatly, from 3.3 for “Moreau” to 27 N for “Minnulara” cherries (Ballistreri et al., 2013). Firmness at harvest of 17 sweet cherry cultivars varied between 2.56 and 4.71 N and was judged acceptable for 73–92% of the panelists (Hampson et al., 2014). Softening is due to an increased peroxidase (POD), polyphenoloxidase (PPO), pectinmethylesterase (PME), polygalacturonase (PG), and β-galactosidase (β-Gal) activities. The level of these enzymes increased around 2 to 2.5-fold during a 5-day storage period causing a damage of cell wall components and subsequent softening (Remón et al., 2003).
The fruit cuticle likely plays an important role with respect to postharvest performance. The sweet cherry fruit cuticle is composed of a cutin polymer matrix, which consists essentially of esterified hydroxy- and epoxyhydroxy fatty acids with a chain length of 16 or 18 C-atoms and embedded in cuticular and surface-deposited epicuticular waxes (Peschel et al., 2007). During cherry development, the levels of C16 and C18 monomers decreased (Peschel et al., 2007), but increased during cold storage (Belge et al., 2014). During early sweet cherry fruit development, the cessation of cuticular membrane deposition is due to downregulation of genes involved in cuticular membrane deposition, such as PaATT1, PaCER1, PaGPAT4/8, PaLACS 1, PaLACS2, PaLCR, PaLipase, PaLTPG1, PaWINA, and PaWINB (Alkio et al., 2012). The main function attributed to the fruit cuticle is limiting water permeability, susceptibility to infections, and physiological disorders such as fruit cracking. The fruit cuticle composition is also associated with postharvest water loss from fruit respiration and firmness changes (Lara et al., 2014). Cherries have a high respiration rate which leads to softening that is partly due to water loss. Dehydration during postharvest storage might induce PacNCED1 transcription and the accumulation of ABA resulting in ethylene production and subsequent fruit senescence (Luo et al., 2014). Water loss may lead to an increased susceptibility to infections and mechanical injuries (Esti et al., 2002). During postharvest storage, in particular for longer periods, fungal spoilage can lead to considerable economic losses (Conte et al., 2009; Romanazzi et al., 2009). The development of off-flavors is promoted by bacteria and fungi due to ethanol and acetaldehyde synthesis (Esti et al., 2002).
Cherry fruit taste attributes, sweetness, and sourness, are important for consumer acceptance. Sweetness can be expressed as soluble solids content (SSC), sourness as titratable acidity (TA) with the ratio (SSC/TA) regarded as overall taste attribute (Guyer et al., 1993; Crisosto et al., 2002). SSC values varied from 12.3 to 23.5°Brix (González-Gómez et al., 2009) and varied from 14.7 to 23.7°Brix for Spanish sweet cherry cultivars (Pérez-Sánchez et al., 2010). SSC values ranged from 18.1 to 19.3 and from 17.8 to 19.8°Brix for Brazilian and Chinese sweet cherries, respectively (Rios de Souza et al., 2014; Wen et al., 2014). TA values ranged from 0.20 in “Lapins” to 0.28 for the Canada Giant cultivars (Vavoura et al., 2015). High TA affects taste when the SSC value is below 16°Brix in “Brooks” or below 13°Brix in “Bing” (Crisosto et al., 2003). The optimal SSC/TA ratio is between 1.5 and 2.0, with SSC values ranging between 17 and 19°Brix (Kappel et al., 1996).
Sweetness and flavor intensity are important parameters for sweet cherry liking (Romano et al., 2006). The most important sensory features are related to the ripening stage, parameters linked with accumulation of organic acids and aromatic alcohols (Serradilla et al., 2012). Several pathways in the biosynthesis of volatiles originate from amino acids, membrane lipids, and carbohydrates contributing for the ripe fruit flavor (Hadi et al., 2013). The aroma profile of sweet cherries is mainly the result of a complex mixture of alcohols, carbonyls, and organic acids (Mattheis et al., 1992; Girard and Koop, 1998; Bernalte et al., 1999; Zhang et al., 2007; Serradilla et al., 2012; Vavoura et al., 2015). Hexanal and ethyl-2-hexenal are the most relevant compounds in the aroma profile of sweet cherries, that together with ethyl-2-hexen-1-ol, are associated with fresh green odors and green notes (Zhang et al., 2007; Serradilla et al., 2012). Benzaldehyde, originates from the enzymatic hydrolysis of amygdalin, is likely the main contributor to the characteristic flavor of sweet cherry (Zhang et al., 2007). Other important contributors are hexanoic acid, described as floral (Pherobase, 2007), and acetic acid, the main volatile acid found in sweet cherry fruits (Serradilla et al., 2012). Significant changes in volatile composition have been observed during ripening of sweet cherry (Zhang et al., 2007; Serradilla et al., 2012). The branched-chain alcohols, 3-methyl-3-buten-1-ol, and 3-methyl-2-buten-1-ol increase during ripening, whereas the organic acids, tetradecanoic and hexadecanoic acid, decrease during ripening, which may be due to reactions between alcohols and organic acids, catalyzed by alcohol acyltransferases. These enzymes seem to play a crucial role in ester biosynthesis (Olías et al., 1995; Serradilla et al., 2012). High variation was recorded in the composition of volatiles amongst four sweet cherry cultivars grown in Spain (Serradilla et al., 2012). “Sweetheart” cherries were mainly characterized by higher levels of organic acids, such as 9-hexadecenoic acid, hexadecanoic acid, and aromatic alcohols and “Ambrunés” cherries by higher sweetness levels and presence of aliphatic alcohols. “Pico Colorado” cherries showed higher levels of hexanal and “Pico Negro” cherries were characterized by higher levels of branched alcohols, mainly 3-methyl-2-buten-1-ol and aromatic aldehydes, such as benzaldehyde. Similar research with four sweet cherry cultivars grown in Greece reported that “Ferrovia” and “Skeena” cherries showed higher levels of carbonyl compounds (2-propanone and 2-hexenal) and alcohols compared to “Lapins” and “Canada” cherries (Vavoura et al., 2015).
Health Promoting Compounds
The role of several classes of health promoting compounds that are present in sweet cherry, lowering the risk of cancer, cardiovascular disease, diabetes, and other inflammatory diseases, has been recognized and is a field of many animal and now increasingly also epidemiological studies (McCune et al., 2010).
Sweet cherry phenolic compounds exhibit high antioxidant activity (Gonçalves et al., 2004a; Serrano et al., 2005; Kelebek and Selli, 2011; Serra et al., 2011). These compounds consist of flavonoids, flavan-3-ols, and flavonols and non-flavonoid compounds like hydroxycinnamic and hydroxybenzoic acids (Macheix et al., 1990; Gao and Mazza, 1995; Gonçalves et al., 2004a). Phenolic compounds, concentrated in the fruit skin, increase during ripening together with polyphenolic compounds and anthocyanins that color the cherry skin from green to red (Mozetič et al., 2004; Gonçalves et al., 2007). Anthocyanins and flavonols contribute to sensory and organoleptic properties of fruits (Ferretti et al., 2010). Table 1 presents an overview of the levels of phenolic compounds found in several sweet cherry cultivars. The most abundant phenolic compounds are anthocyanins (Mozetič et al., 2002; Gonçalves et al., 2004a; Usenik et al., 2008) such as cyanidin-3-O-rutinoside and cyanidin-3-O-glucoside, peonidin-3-O-rutinoside and glucoside, as well as pelargonidin-3-O-rutinoside (Gonçalves et al., 2007). Anthocyanins have health promoting properties. For instance, cyanidin-3-O-rutinoside slows down absorption of carbohydrates which may help prevent or treat diabetes mellitus (Adisakwattana et al., 2011) and cyanidin-3-O-glucoside showed cardio-protective effects by reducing blood lipid levels (Xia et al., 2005). Several studies reported higher phenolic content (Gonçalves et al., 2004a; Serrano et al., 2009), SSC, TA and antioxidant activity (Serrano et al., 2009) in ripe cherries than in partially ripe. Sweet cherry contains phenolic acids such as hydroxycinnamic acid derivatives (neochlorogenic, p-coumaroylquinic, and chlorogenic acids; Gonçalves et al., 2004a; Usenik et al., 2010; Liu et al., 2011), flavonols (quercetin-3-glucoside, quercetin-3-rutinoside, and kaempferol-3-rutinoside) and flavan-3-ols (catechin and epicatechin), as shown in Table 1 (Gonçalves et al., 2004a; Mozetič et al., 2006; Usenik et al., 2008; Jakobek et al., 2009). Consumption of cherries might induce health benefits such as inhibition of tumor growth (Kang et al., 2003; Serra et al., 2011), inhibition of inflammation (Seeram et al., 2001; Jacob et al., 2003) and protection against neurodegenerative diseases (Kim et al., 2005). These fruits are also considered an excellent source of polyphenols, such as tannins (Tomás-Barberán and Espín, 2001). Tannins can be classified in hydrolysable tannins (gallic acid polymerization) and condensed tannins or proanthocyanidins (catechin polymerization) (Macheix et al., 1990). Tannins are also secondary metabolites that confer astringency and have health-promoting properties (Tomás-Barberán and Espín, 2001; McCune et al., 2010). Tannin content ranged from 32 to 75 mg 100 g−1 of fresh weigh for Serbian sweet cherry cultivars (Prvulović et al., 2012). Sweet cherry extracts might be a serious candidate to prevent oxidative stress-induced disorders like intestinal inflammation disorders and neuronal cell death (Matias et al., 2016).