BEAN QUALITY SYSTEM
Commodities / Snap Beans
Flavor | Texture | Color | Size | Shape | Defects and Disease | Shelf Life | Nutritive Value
MW Vegetable Production Guide | Postharvest Information (UC Davis) | USDA Grade Standards
Snap bean quality is a combination of appearance and physical condition. The beans should be well formed, uniform, straight, crisp, have good color and no defects. Except for color and length there is little distinction among varieties. Some varieties have a larger diameter than others or may appear smoother in texture. Quality characteristics of interest to the grower include plant vigor, resistance to lodging, uniformity of set, yield potential, ease of harvest and disease resistance.
Fresh snap beans have a relatively uniform flavor. There are differences among varieties but they are difficult to quantify. There is a noticeable difference between snap beans and romano beans, pole beans and White Half Runner beans. Snap beans that have become wilted, have chilling injury or disease may have a poor flavor.
Snap beans increase in fiber as they mature. There are also significant differences in fiber content among varieties. Fresh market snap beans generally have a higher fiber content than processing varieties. Higher fiber content results in less breakage during harvest and handling. Fiber development parallels seed development in those varieties having fiber. When seed development is noticeable in the pod by the swelling each seed causes in the pod, the beans are near the limit of suitability for marketing. Seeds are of different sizes. Small seeded varieties may have a longer harvest window than large seeded varieties.
Snap beans are green or yellow. Horticultural beans and other specialty beans may be purple or variegated. Green snap beans are light, medium or dark green. Dark colored beans tend to mask some russeting and other minor defects that are more evident on light colored beans. Yellow beans, sometimes called wax beans, may be light yellow to an intense, almost gold color. Seeds are either white or dark; dark seeded varieties are often early.
Snap beans are bright colored at harvest when the pods are turgid. Water loss will cause the pods to become wilted and dull. Chilling injury will cause loss of color intensity.
Fresh market snap bean length is 5 to 7 inches with most being 5 to 6.5 inches. Diameter in fresh market sales is not related to any grade standard. There are grade standards for processing snap beans related to sieve size (diameter). Sieve sizes range from 14.5- to 18.5-64ths of an inch (sieve 1) to 27- to 30-64ths of an inch (sieve 6). Typically harvest for processing begins when 50% of the beans are sieve size 4 (21- to 24- 64ths). There are "petite" size snap beans that are mature at 4 inches long. They are used for whole pack beans by processors.
Curved pods and pods with missing seeds are the most common defects in shape. Slightly curved pods are not a quality problem, however the more the pods are curved the less uniform they appear. Straight pods provide a better appearance. The percentage of curved pods increases in plants with pods set low in the plants or plants that lodge allowing pods to touch the soil. The pod cross-section may be nearly round or slightly oval. The pods are more likely to have missing seeds if the plant is under stress at the time of pod set.
Snap beans that grow under optimum soil, temperature and moisture conditions will have fewer curved pods and missing seeds. Many varieties are subject to lodging if the plant grows too luxuriantly and has a large crop. Lodging increases the number of pods touching the soil and results in a higher percentage of curved pods. For this reason plants that are upright and have a high set are desirable. Pod set is concentrated in most bush beans, however bloom takes place over several days. High temperature during bloom (over 85˚F) can result in poor set or a "split set". There are differences among varieties in susceptibility to split set.
Defects and Disease top
The most common diseases affecting the pods are white mold and gray mold. Control recommendations can be found in the Midwest Vegetable Production Guide for Commercial Growers, or through your local Cooperative Extension Service.
White Mold (Sclerotinia sclerotiorum) usually develops after there is a full canopy of leaves with moist soil and temperatures 50˚ to 80˚ F (55˚ to 60˚F optimum). The infection takes place in the field but can be controlled with sprays at bloom.
Gray Mold (Botrytis cinerarea) can occur in the field or in storage. Gray mold is most likely to develop when there is a full canopy of leaves creating a micro-climate with high humidity.
European Corn Borer can infest the pods of snap bean. Monitoring and spray programs are effective in preventing the problem.
Shelf Life top
Decreased quality during postharvest handling is most often associated with water loss, chilling injury, and decay.
It is important to remove field heat as soon as possible to prevent water loss. Most shippers will use hydro cooling to achieve temperatures of 41˚ to 45˚F; a shelf life of 8-12 days can be expected if these temperatures are maintained at 95% to 100% humidity. Limpness and shrivel are noticeable if more than a 5% water loss occurs.
Chilling injury will occur at storage temperatures below 41˚F. Exposure to ethylene at usual storage temperatures causes loss of green pigment and increased browning.
BEAN QUALITY CONTROL
Savita Chaurasia, in Nutritional Composition and Antioxidant Properties of Fruits and Vegetables, 2020
17.2.9 Additional health benefits of green beans
Green beans are useful for menstruating women and also for those who can be at the risk of vitamin B or iron deficiencies.
Green beans are rich in fiber and low in fats; hence these beans are an ideal food for those on weight-loss diets. Adding green beans to your diet ensures a healthy and nutritious food without extra calories. It can also be added to salads and soups, in addition to other nutritious vegetables.
Development of fetus and especially its organs. Green beans help in the development of the baby’s heart during pregnancy and also help to provide protection from conditions such as asthma later on in life.
Constituents like flavonoids and carotenoids are also available in green beans. These have strong antiinflammatory properties and help in alleviating conditions like gout.
Green beans have a high iron content and are an ideal food during pregnancy as well as breastfeeding after pregnancies.
Green bean pods have a moderate diuretic effect which stimulates urine flow and also helps in elimination of toxins from the body.
Studies have also shown that dusting of powdered green beans over eczema affected areas relieve itching and dryness.
Green beans have high vitamin C content which boosts the immune system.
Green beans also have antiaging properties. Beans contain vitamin A that helps to reduce the effects of ageing. A diet with a high green beans intake can reduce the chances of skin-related deceases.
It is noteworthy to mention that it is not just the individual vitamins, minerals, or antioxidants alone that make the green beans an important part of our diet, but the combined effect of all nutrients that makes them important. So, we cannot replace green beans with dietary supplements because they cannot replicate all the benefits of green beans.
Quality Attributes Limiting Snap Bean (Phaseolus vulgaris L.) Postharvest Life at Chilling and Non-chilling Temperatures
‘Opus’ and ‘Leon’ snap beans were harvested, hydrocooled, held for 2 to 7 days at five temperatures and evaluated for quality attributes. The objectives of this work were to obtain quality curves at chilling and non-chilling temperatures, identify for each temperature which quality attributes limit snap beans marketability, and determine the remaining compositional value at the point the snap beans had reached the minimum acceptable quality for sale. Results from this study showed that temperature had a significant effect on the shelf life and overall quality of snap bean. Snap beans stored at temperatures higher than 10 °C were less green, softer and more shriveled, had higher weight loss, and lower acidity, soluble solids, ascorbic acid, and chlorophylls contents than those stored at lower temperatures. When stored at 1, 5, and 10 °C, ‘Leon’ snap beans developed chilling injury (CI), whereas no visual symptoms were noticeable in ‘Opus’ snap beans. Although CI might have indirectly affected the quality of ‘Leon’ snap beans, it was not considered a sensory quality-limiting factor. Overall, weight loss was the first non-sensory quality attribute to reach the limit of acceptability, whereas firmness was the first sensory quality attribute, followed by color, to reach the limit of acceptability and therefore limited the shelf life of ‘Opus’ and ‘Leon’ snap beans cultivars. As a result of excessive water loss and accelerated softening, shelf life of both snap bean cultivars was relatively short, ranging from 1 to 3.5 days, depending on the temperature and cultivar. Furthermore, the compositional value was considerably reduced at the point of poor sensory quality. The high weight loss obtained for beans stored at all temperatures suggests that the use of a film wrap may help create a high relative humidity and therefore reduce water loss, maintain better overall quality, and extend the shelf life of snap beans. Overall, maximum shelf life and best quality were obtained when ‘Opus’ and ‘Leon’ snap beans were stored at 10 °C.
Keywords: storage; chilling injury; fruit quality; fruit composition
The continuous development of improved snap bean cultivars throughout the years has provided germplasm with wide variety of colors, textures, shapes, and sizes to meet the growing conditions and taste preferences of consumers from many different regions (Orzolek et al., 2000). In 2001, the collection of the Food and Agriculture Organization included 26,500 Phaseolus vulgaris entries, reflecting a large genetic diversity (CIAT, 2001). Such diversity can explain the wide variation in shelf life, resistance to chilling temperatures as well as variability in physical and chemical attributes. Generalization of sensory and compositional attributes among snap bean cultivars is difficult. Quality differentiation among individual fruits and vegetables by consumers is based primarily on appearance (Zind, 1989). In snap beans, color is an important feature, which changes from a desirable bright green to an objectionable yellowish color (Trail et al., 1992). Textural attributes and loss of chlorophylls are also excellent indices of quality because they parallel color changes, loss of ascorbic acid, and off-flavor development (Cain et al., 1953; Martinez et al., 1995).
Quality at harvest and environmental conditions, particularly temperature, during the postharvest period greatly affect the shelf life and quality of snap beans. It is well recognized that good temperature management is the simplest way to maintain a high-quality appearance as well as to delay losses in the nutritional value of fruits and vegetables in general (Nunes, 2008a; Nunes and Emond, 2002). As a result of their high respiration rate and sensitivity to chilling temperatures, snap beans are very perishable (Costa et al., 1994). Therefore, for a maximum shelf life of 8 to 12 d, recommended storage temperatures range from 5 to 7.5 °C with 95% to 100% relative humidity (Cantwell and Suslow, 2010; Hardenburg et al., 1986). When stored at temperatures above the recommended, snap beans will show discoloration, yellowing, loss of firmness, and a leathery appearance, whereas when stored at temperatures below the recommended, the pods will develop chilling injury (CI) symptoms such surface pitting, diagonal brown streaks, dull appearance, and breakdown from microorganisms after transfer to warm temperature (Nunes, 2008a; Watada and Morris, 1966b). However, sensitivity to chilling temperatures seems to be cultivar-dependent (Watada and Morris, 1966a). In addition to good temperature management, minimizing the time between harvest and sale prevents decrease in chlorophylls and vitamin C contents, increased weight loss resulting from loss of moisture, and reduced crispness (Sistrunk et al., 1989).
Much of the research work done on snap beans has been directed to the processing industry (Ferreira et al., 2006; Freeman and Sistrunk, 1978; Gould et al., 1951; Kahn and McGlynn, 2009; Woodruff et al., 1962) with a few recent studies on fresh produce (Cano et al., 1998; Costa et al., 1994; Kahn and McGlynn, 2009; Martinez et al., 1995; Nunes et al., 2001). No data were however found in the literature regarding quality curves for snap beans stored at various temperatures. In fact, the few previous published studies report the optimum storage temperature for snap beans (Monreal et al., 1999; Trail et al., 1992) or the response to storage at chilling temperatures (Abou Aziz et al., 1976; Gorini et al., 1974; Watada and Morris, 1966a, 1966b) rather than changes in quality that develop over time and over a wide range of temperatures. In addition, previous studies have shown that the quality attributes that limit shelf life may vary depending on the commodity and storage temperature and therefore one single attribute should not be used to determine the end of the shelf life of a particular fruit or vegetable (Nunes et al., 2004, 2007; Proulx et al., 2005). Yet again, no information was found regarding the most important sensory quality attributes that determine the limits of marketability for snap beans stored at various temperatures. Finally, although the sensory quality of a specific commodity may still be considered acceptable for sale or consumption, the remaining compositional value might have been already significantly reduced.
The objectives of this work were to: 1) create quality curves for snap beans stored at chilling and non-chilling temperatures; 2) identify which sensory quality attribute limits the shelf life and marketability of snap beans when stored at chilling and non-chilling temperatures; and 3) evaluate the remaining compositional value at the point the snap beans had reached the minimum acceptable quality for sale.
Materials and Methods
Plant material and storage conditions.
Snap beans (Phaseolus vulgaris L.) cvs. Opus and Leon were harvested at commercial maturity (i.e., bright green, tender fleshy and with small green immature seeds) from a commercial field in Homestead, FL. A total of two harvests (experiments) were conducted during the winter season (i.e., February to March). Snap beans were removed from the field with minimal delay after harvest, commercially hydrocooled, and transported to the laboratory in Gainesville, FL, within ≈6 h. Beans were then sorted by size, color, and freedom of defects. ‘Opus’ snap bean pod weight averaged 6.0 g, whereas ‘Leon’ snap bean pod weight averaged 10.0 g. A total of 2160 snap bean pods per cultivar were selected for uniformity of color and freedom from defects, weighed, and carefully distributed by 144 polyethylene terephthalate vented clamshells (capacity ≈453 g) (Pactiv Corporation North America, Lake Forest, IL) containing 15 snap bean pods each. To create a relative humidity (RH), without however modifying the atmosphere around the pods, the clamshells were placed inside open large opaque plastic bags (Glad Products Company, Amherst, VA Amherst, VA AmherstVA,). Clamshells containing the selected snap beans were then stored at 0.5 ± 0.5 °C and 90.0 ± 3.5% RH, 5.0 ± 0.5 °C and 93.2 ± 3.5% RH, 10.0 ± 0.5 °C were 94.0 ± 3.5% RH, 15 ± 0.5 °C and 92.0 ± 3.5% RH, and 20.0 ± 0.5 °C and 93.0 ± 3.5% RH. For ease of interpretation, temperatures were rounded to 1, 5, 10, 15, and 20 °C.
Temperature and relative humidity monitoring.
The temperature inside the plastic bags containing the snap bean trays were monitored throughout storage using Stow Away® XTI02 temperature loggers (–5 to +37 °C) (Onset Computer Corporation, Pocasset, MA). RH was monitored with Stow Away® RH loggers (10% to 95% RH) (Onset Computer Corporation).
Three clamshells containing 15 snap bean pods each (a total of 45 pods) were used for initial sensory quality evaluations (color, browning, firmness, shriveling, and pitting) and immediately frozen to be later used for chemical compositional analysis (pH, titratable acidity, and soluble solids, ascorbic acid, and chlorophylls contents). Fifteen clamshells containing 15 snap bean pods each (a total of 225 pods) were distributed among the five temperature-controlled rooms and reused daily for non-destructive quality evaluations (sensory quality and weight). That is, each day the same three clamshells were removed from their respective temperature to a temperature-controlled room (≈20 °C) for ≈30 min, sensory quality evaluated and weight measured, and then returned to their respective temperature. Likewise, for daily destructive quality evaluations, 105 clamshells containing 15 snap bean pods each (a total of 1575 pods) were distributed among the five temperature-controlled rooms. However, each day, three of these clamshells were removed from their respective temperature and immediately placed inside a –80 °C freezer to be later used for chemical compositional analysis. Finally, to evaluate the effect of storage at 1, 5, and 10 °C on the development of CI symptoms, 21 clamshells containing 15 snap bean pods each (a total of 315 pods) were distributed among the chilling temperatures (a total of seven clamshells per temperature). Each day, one clamshell was removed from each of the chilling temperatures, transferred to 20 °C for 1 additional day, and then CI symptoms (i.e., pitting, rusty spots, and discoloration) were evaluated. In summary, 24 clamshells containing 15 pods each were stored at 15 and 20 °C (three for non-destructive quality evaluations and 21 for destructive quality evaluations) and 31 clamshells containing 15 pods each were stored at 1, 5, and 10 °C (three for non-destructive quality evaluations, 21 for destructive quality evaluations, and 7 for CI evaluation). The total amount of clamshells/snap bean pods was calculated based on a 7-d storage period; however, storage was ended when the quality of the snap beans was considered unacceptable for sale or consumption. Therefore, storage times varied from 2 to 7 d, depending on the cultivar and storage temperature (see “Results and Discussion” section).
Surface color measurements were taken on each individual bean from clamshells designated for sensory evaluation at 5 cm from the bean stem end with a handheld tristimulus reflectance colorimeter (Model CR-300; Minolta Co., Ltd., Osaka, Japan) equipped with a glass light-protection tube with an 8-mm aperture (CR-A33a; Minolta Co., Ltd.) using standard illuminant D65. Color was recorded using the CIE-L*a*b* uniform color space (CIE-Laboratory), L* (lightness), a* (redness), and b* (yellowness) values. Numerical values of a* and b* were converted into hue angle and chroma using the Minolta Color Management Software (1996–1999 CyberSoft SpectraMatch/QC software Version 3.3; CyberChrome, Inc., Stone Ridge, NY).
Sensory quality evaluation of snap beans was performed daily during a 2- to 7-d storage period, depending on the cultivars and storage temperature, always by the same trained person. Surface color, browning severity, shriveling, and CI (i.e., pitting, rusty spots, and discoloration) were determined subjectively using a 1 to 5 visual rating scale, and firmness was determined subjectively based on the whole snap beans resistance to slight applied finger pressure and recorded using a 1 to 5 tactile rating (Table 1). A score of 3 was considered to be the limit of acceptability for sale.
Visual quality scores and descriptors for snap beans.
Table 1.View Table
To compare weight loss and sensory quality attributes, weight loss percentages were converted into a 1 to 5 rating scale. The maximum acceptable weight loss (before considered unmarketable) was set at 5% (Robinson et al., 1975). Ratings for weight loss were as follows: 1 = 10.0% or more weight loss, 2 = 7.5% weight loss, 3 = 5.0% weight loss (maximum acceptable), 4 = 2.5% weight loss, 5 = 0% weight loss. The following formula was used to convert percentage of weight loss into ratings values: [(%weight loss/10 × 4) + 1].
Weight loss of each replicate of 15 snap beans was calculated from the initial weight of beans and after each day during a 2- to 7-d storage period depending on cultivar and storage temperature. Concentrations of chemical constituents were expressed in terms of dry weight to show the differences between temperatures that might be obscured by differences in water content. The following formula was used for water loss corrections: [chemical components (fresh weight) × 100 g/9.7 g (snap beans average dry weight) + weight loss during storage (g)]. Snap beans dry weight was determined by drying three weighed aliquots of homogenized snap bean tissue at 80 °C and until weight stabilized.
pH and titratable acidity.
Chopped snap beans (20.0 g per replicate) were mixed with 10.0 g of distilled water (pH 6.8 to 7.2) and homogenized in laboratory blenders at high speed for 1 min. The homogenates were centrifuged at 800 gn for 30 min, filtered through cheesecloth, and the pH of the juice was determined using a pH meter (Accumet Model 15; Fisher Scientific, Arvada, CO) that had been previously standardized to pH 4 and pH 7. Aliquots (6.0 g) of the juice were diluted with 50 mL distilled water and the titratable acidity determined by titration with 0.1 N NaOH to an end point of pH 8.1 with an automatic titrimeter (Titroline 96; SCHOTT-GERÄTE GmbH, Germany). The results were converted to percent malic acid, the main organic acid in snap beans (Martinez et al., 1995) using the following formula: [(mL NaOH × 0.1 N × 0.064 meq/6.00 g of juice) × 100]. Titratable acidity was expressed in terms of dry weight.
Soluble solids content.
The soluble solids content (SSC) of the resulting clear juice samples (see previously) was measured with a digital refractometer (Palette PR-101, 0 to 45 °Brix; Atago Co. Ltd., Tokyo, Japan) and was expressed in terms of dry weight.
STRESS MAY LEAD TO SNAP BEAN QUALITY PROBLEMS AND YIELD REDUCTION
Snap beans are very susceptible to quality reductions and yield losses when under stress during flowering and early pod development. This is a common problem in hot weather where pollination is affected leading to split sets. We are currently evaluating varieties of snap beans for heat tolerance at the University of Delaware’s research farm at Georgetown with early May and mid-June plantings.
May snap bean plantings commonly avoid hot weather and produce high yields with good quality. However, in 2017, cold, wet weather after planting and high incidence of root rot in our trials has resulted in reduced plant vigor, shorter plants, reduced yield, and poor pod quality.
Early season stress is not uncommon and typically we recommend the use of seed already treated with an approved seed treatment with a fungicide for Rhizoctonia and Fusarium control such as Maxim 4FS, a second fungicide for Pythium control such as Apron XL LS and an improved insecticide for seed corn maggot control. It is also recommended that April and early May snap bean plantings go into in lighter soils with good drainage.
Fresh Snap Beans Grades and Standards
U.S. Fancy consists of beans of similar varietal characteristics which are of reasonable and fairly uniform size, well formed, bright, clean, fresh, young and tender, firm, and which are free from soft rot and free from damage caused by leaves, leaf stems, other foreign matter, hail, disease, insects or mechanical or other means. (See §51.3835.)
U.S. No. 1 consists of beans of similar varietal characteristics which are of reasonable size, fairly well formed, fairly bright, fresh, fairly young and tender, firm, and which are free from soft rot and free from damage caused by dirt, leaves, leafstems, other foreign matter, hail, disease, insects or mechanical or other means. (See §51.3835.)
U.S. No. 2 consists of beans of similar varietal characteristics which are fairly fresh, firm, not overmature, and which are free from soft rot and free from serious damage caused by dirt, leaves, leaf stems, other foreign matter, hail, disease, insects or mechanical or other means. (See §51.3835.)