BROCOLLI QUALITY MANAGEMENT
Head diameter and compactness; all florets (beads) should be closed.
Good quality broccoli should have dark or bright green closed florets. The head should be compact (firm to hand pressure), with a cleanly cut stalk of the required length. There should be no yellow florets and there should be no discoloration on the stem bracts.
Temperature & Controlled Atmosphere
Low temperature is extremely important to achieve adequate shelf-life in broccoli. A temperature of 0°C (32°F) is required to optimize broccoli storage life (21-28 days). Heads stored at 5°C (41°F) can have a storage life of 14 days; storage life at 10°C (50°F) is about 5 days. Broccoli is usually rapidly cooled by liquid-icing the field-packed waxed cartons. Hydrocooling and forced-air cooling also can be used, but temperature management during distribution is more critical than with iced broccoli.
Freezing Injury. Broccoli will freeze if stored at -0.6°C (30.6°F) to -1.0°C (30°F). This may also occur if salt is used in the liquid-ice cooling slurry. Frozen and thawed areas on the florets appear very dark and translucent, may discolor after thawing and are very susceptible to bacterial decay.
Optimum Relative Humidity
Rates of Respiration
Broccoli heads have relatively high respiration rates:
Temperature 0°C (32°F) 5°C (41°F) 10°C (50°F) 15°C (59°F) 20°C (68°F)
ml CO2/kg·hr 10-11 16-18 38-43 80-90 140-160
The respiration rates of florets are slightly more than twice the rates of the intact heads.
To calculate heat of production multiply ml CO2/kg·hr by 440 to get Btu/ton-day or by 122 to get kcal/metric ton-day.
Rates of Ethylene Production
Responses to Ethylene
Broccoli is extremely sensitive to exposure to ethylene. Floret yellowing is the most common symptom. Exposure to 2 ppm ethylene at 10°C (50°F) reduces shelf-life by 50%.
Responses to Controlled Atmospheres (CA)
Broccoli can be benefitted by 1-2% O2 with 5-10% CO2 atmospheres at a temperature range of 0-5°C (32-41°F). Although under controlled conditions such low O2 levels extend shelf-life, temperature fluctuations during commercial handling make this risky as broccoli can easily produce offensive sulfur-containing volatiles. As a result, a high rate of air exchange is recommended in standard marine container shipments of broccoli. Most modified atmosphere packaging for broccoli is designed to maintain O2 at 3-10% and CO2 at about 7-10% to avoid the development of these undesirable off-odor volatiles.
Temperature & Controlled Atmosphere Photos
Title: Ethylene Induced Yellowing of Broccoli
Physiological and Physical Disorders
Hollow Stem. An open area in the stem at the cut surface which may become discolored and decay; growing conditions and variety selection affect development of this disorder.
Floret (bead) Yellowing. The florets are the most perishable part of the broccoli head; yellowing may be due to overmaturity at harvest, high storage temperatures, and/or exposure to ethylene. Any development of yellow beads ends commercial marketability. Bead yellowing due to senescence should not be confused with the yellow-light green color of areas of florets not exposed to light during growth, sometimes called "marginal yellowing".
Brown Floret (bead). Is a disorder in which areas of florets do not develop correctly, die and lead to brown discolored areas. This is thought to be caused by plant nutritional imbalances.
Rough handling at harvest can damage the florets and increase decay. The force used to apply the water-ice slurry for cooling can also damage the florets on the heads and increase susceptibility to bacterial decay.
Bacterial decay. Various soft-rot causing organisms (Erwinia, Pseudomonas) may affect broccoli shelf-life. Rots due to these organisms are usually associated with physical injury.
Fungal pathogens. Although not as common as bacterial rots, gray mold rot (Botrytis cinerea) and black mold (Alternaria spp.) can infect broccoli heads; this may occur under rainy, very cool growing conditions.
Storage life varies considerably among broccoli cultivars. Shelf-life (appearance of any yellow beads = end of shelf-life) may vary from 12 to >25 days depending on cultivar: Shelf-life of different broccoli cultivars stored at 5°C (41°F), and 95% RH:
QUALITY BROCCOLI SUPPLIER
Receiving Information: Good quality broccoli should have fresh-looking, light green stalks of consistent thickness. Bud clusters should be compact and dark green with some purple tinge. When pulled apart, some bud clusters may appear yellow around the edges. This does not affect product quality; it simply means that the clusters were not exposed to sunlight during growing. Avoid broccoli with open, flowering, discolored, or water-soaked bud clusters and tough, woody stems. Handle broccoli with care to avoid damage to bud clusters. To revive slightly wilted broccoli, apply ice directly to bunches or plunge in cold water, drain, and place in cooler. Broccoli is sensitive to ethylene gas; exposure may cause bud clusters to turn yellow or drop off. Keep away from ethylene producing fruits and ripening rooms. Holding broccoli for long periods of time may cause discoloration, loss of buds or general softening of the product. For best quality, use broccoli soon after receiving. Storage/Handling: Temperature/humidity recommendation for short-term storage of 7 days or less: Temperature: 32 F, 0 C. Relative humidity: 95-100%. Mist: lightly (unpackaged). Typical shelf life: bunched 10 to 14 days, packaged 14 to 16 days. Ethylene-sensitive. Do not store or transport with commodities that produce ethylene. Moderately sensitive to freezing injury. Dunking in cold water can revive slightly wilted broccoli.
Calabrese is the most predominant variety sold commercially and noted for their bright green stalks with compact bud clusters that are dark green with some purple tinge. Broccoli is believed to have originated in southern Italy; and has a long history of cultivation, having been developed by the Romans from wild cabbage. The Romans had high esteem for this vegetable, which to this day is often associated with Italian cuisine. Broccoli was grown for its floral shoots in Asia Minor, and brought by navigators to Italy, where it was subsequently developed and improved.
BROCCOLI INSPECTION QUALITY
Complex Horticultural Quality Traits in Broccoli Are Illuminated by Evaluation of the Immortal BolTBDH Mapping Population
Zachary Stansell1,2*, Mark Farnham3 and Thomas Björkman1,2
1School of Integrative Plant Science, Cornell University, Ithaca, NY, United States
2Cornell Agritech, Cornell University, Geneva, NY, United States
3USDA-ARS Vegetable Laboratory, Department of Horticulture, Charleston, SC, United States
Improving horticultural quality in regionally adapted broccoli (Brassica oleracea var. italica) and other B. oleracea crops is challenging due to complex genetic control of traits affecting morphology, development, and yield. Mapping horticultural quality traits to genomic loci is an essential step in these improvement efforts. Understanding the mechanisms underlying horticultural quality enables multi-trait marker-assisted selection for improved, resilient, and regionally adapted B. oleracea germplasm. The publicly-available biparental double-haploid BolTBDH mapping population (Chinese kale × broccoli; N = 175) was evaluated for 25 horticultural traits in six trait classes (architecture, biomass, phenology, leaf morphology, floral morphology, and head quality) by multiple quantitative trait loci mapping using 1,881 genotype-by-sequencing derived single nucleotide polymorphisms. The physical locations of 56 single and 41 epistatic quantitative trait locus (QTL) were identified. Four head quality QTL (OQ_C03@57.0, OQ_C04@33.3, OQ_CC08@25.5, and OQ_C09@49.7) explain a cumulative 81.9% of phenotypic variance in the broccoli heading phenotype, contain the FLOWERING LOCUS C (FLC) homologs Bo9g173400 and Bo9g173370, and exhibit epistatic effects. Three key genomic hotspots associated with pleiotropic control of the broccoli heading phenotype were identified. One phenology hotspot reduces days to flowering by 7.0 days and includes an additional FLC homolog Bo3g024250 that does not exhibit epistatic effects with the three horticultural quality hotspots. Strong candidates for other horticultural traits were identified: BoLMI1 (Bo3g002560) associated with serrated leaf margins and leaf apex shape, BoCCD4 (Bo3g158650) implicated in flower color, and BoAP2 (Bo1g004960) implicated in the hooked sepal horticultural trait. The BolTBDH population provides a framework for B. oleracea improvement by targeting key genomic loci contributing to high horticultural quality broccoli and enabling de novo mapping of currently unexplored traits.
Improvement of broccoli and other Brassica oleracea vegetables (cauliflower, cabbage, kale, Gai lan, Brussels sprouts, kohlrabi, and collard) is constrained by complex interactions of many genes affecting plant architecture, developmental processes, and yield. B. oleracea vegetable crop groups have benefited from a number of advances in plant biotechnology, gradually increasing the overall understanding of these quality-based traits. Specifically, diversity and domestication processes (Cheng et al., 2016; Stansell et al., 2018; Yousef et al., 2018; Li et al., 2019) have been clarified, next-generation sequencing and high-quality reference genomes (Liu et al., 2014; Parkin et al., 2014; Golicz et al., 2016) have expedited discovery of molecular markers associated with key traits, and diverse mapping populations segregating for these traits have been characterized (Kianian and Quiros, 1992; Landry et al., 1992; Camargo and Osborn, 1996; Ramsay et al., 1996; Bohuon et al., 1998; Hu et al., 1998; Lan and Paterson, 2000; Sebastian et al., 2000; Lan and Paterson, 2001; Axelsson et al., 2001; Li et al., 2003; Gao et al., 2007; Brown et al., 2014; Lee et al., 2015a; Li et al., 2015). For example, projects integrating these tools such as the Eastern Broccoli Project (SCRI No. 2010-51181-21062) and the USDA Vegetable Brassica Research Project (CRIS No. 6080-21000-019-00D) have developed heat-tolerant broccoli germplasm adapted to novel environments, reducing costs and enabling more sustainable production models (Atallah et al., 2014; Farnham and Björkman, 2011).
A current limitation in B. oleracea vegetable crop improvement is a lack of publicly available mapping populations, constraining information integration across research programs. Attempts to unify existing maps have been limited due to variable germplasm, different marker types, and linkage group nomenclature (Hu et al., 1998). Furthermore, these populations are often difficult to maintain due to self-incompatibility (Farnham, 1998; Bohuon et al., 1998; Sebastian et al., 2000; Pink et al., 2008; Walley et al., 2012).
To address these issues, the double-haploid (DH) BolTBDH population was developed from a cross between morphologically distinct parents (B. oleracea var. alboglabra × B. oleracea var. italica) that segregates for horticultural quality traits specific to broccoli (Iniguez-Luy et al., 2009). BolTBDH offers several distinct advantages over other mapping populations: a large sample size (N∼175), a high degree of self-compatibility, and a short generation time. The rapid-cycling parental taxa ‘TO1000DH3’ (P1; var. alboglabra) is the reference organism for the B. oleracea v.2 genome (Parkin et al., 2014). ‘Early Big’ (P2; var. italica) has been evaluated in previous studies (Li et al., 2003; Gao et al., 2005; Tortosa et al., 2018). Moreover, both P1 and P2 and included in the B. oleracea pangenome (Golicz et al., 2016). Furthermore, this population has already been used to investigate the genetic control of important traits: glucosinolate content (Sotelo et al., 2014), organ-specific phenylpropanoid metabolism (Francisco et al., 2016), antioxidant content (Sotelo Pérez et al., 2014), and black rot (Xanthomonas campestris pv. campestris) resistance (Iglesias-Bernabé et al., 2019). Under standard greenhouse conditions, BolTBDH lines will typically produce self-seed without the need for hand pollinations. The work presented here increases the value of this population by generating many high-quality genome-wide SNP markers and generating robust phenotypes for 25 horticultural quality traits.
The BolTBDH population provides an unique opportunity to evaluate the genetic basis of the heading broccoli phenotype due to the marked dissimilarity between the parental lines: P1 is rapid-flowering (∼ 65 days to flowering) and exhibits a leafy, non-head-forming inflorescence, whereas P2 is relatively late-flowering (∼ 85 days to flowering) and exhibits a heading broccoli phenotype characterized by extensive meristem proliferation during floral bud development and internode elongation (Björkman and Pearson, 1998). While considerable work has investigated head formation under optimal and heat-stressed conditions (Duclos and Björkman, 2008; Farnham and Björkman, 2011; Hasan et al., 2016; Lin et al., 2019), the exact genetic basis of this phenotype remains elusive (Axelsson et al., 2001; Li et al., 2003; Gao et al., 2007; Okazaki et al., 2007; Razi et al., 2008; Matschegewski et al., 2015; Irwin et al., 2016). There is a growing consensus of the central importance of the homologous flowering timing MADS-box transcription factor FLOWERING LOCUS C (BoFLC) in regulating the reproductive transition by inhibiting downstream BoSOC1 and BoFT expression; in turn, delaying a suite of floral-identity genes including BoLFY, BoAP1, and BoCAL (Lin et al., 2018). The genetic basis of the heading broccoli phenotype could be explained by a number of models: simple control by one or several genes, a constrictive-conditional model where multiple genetic factors must be present, or a pleiotropic model, where several key developmental genes would underlie the broccoli heading phenotype and be further modified by additional downstream factors. Under a simple control model, the heading broccoli phenotype would exhibit qualitative control by a limited number of QTL. Under a purely constrictive-conditional model, the broccoli heading phenotype would occur only when a minimum set of independent factors were present. Under a purely pleiotropic model, a small number of developmental loci or genes are implicated in heading quality traits with epistatic interactions with additional loci.
When breeding multiple quality traits in horticultural crops, it is often challenging to determine the degree that individual traits contribute to the overall quality of these crops when predictor traits are correlated. Relative-importance analyses (RIA) allows quantification of the proportional contribution of a predictor variable to the overall quality-model R2, considering both unique and joint contributions with other variables (Gromping, 2006) and may be used to establish breeding priorities within a horticultural context (Stansell et al., 2017). Within this study, RIA was used to evaluate the independent contribution of individual traits to overall horticultural quality.
Therefore, our main objectives were to: a) characterize the phenotypic variation of horticulturally important traits within the BolTBDH population; b) produce a reference set of robust and high-quality BolTBDH markers; c) identify optimal QTL models to best explain key horticultural quality traits important to broccoli germplasm; and d) identify which candidate B. oleracea developmental genes collocate with observed QTL.
Materials and Methods
The BolTBDH population was generated via anther culture from the parental lines ‘TO1000DH3’ DH (P1; B. oleracea var. alboglabra) × ‘Early Big’ DH (P1; B. oleracea var. italica) (Iniguez-Luy et al., 2009). Seed was provided by the USDA Vegetable Laboratory in Charleston, SC. All initial lines (N = 202; P1 and P1 inclusive) were increased in 2016 and closed-bud pollinations were made to verify selfing integrity. Except for P1 in Y1 due to inadequate seed quality, all lines were sown into 128 cell trays May 11 in Y1 and May 9 in Y2. Seedlings were grown in a greenhouse and transplanted into Lima silt loam fields in Geneva, NY on May 28–29 in Y1 and June 8–11 in Y2. All lines were divided into four randomized replications and transplanted onto raised beds with each plot containing 10–12 plants per genotype. Drip irrigation was applied as needed and any additional cultural practices were as previously described (Farnham and Björkman, 2011). Hourly weather data was collected locally at Cornell AgriTech (Figure S1).
Plots were evaluated daily and deemed mature when 1/3 of the plants reached a heading or heading-equivalent stage. Traits within six classes considered important to broccoli or other B. oleracea crop groups were chosen: architecture, biomass, bud morphology, leaf morphology, head quality, and phenology (Table 1; Figure 1; Stansell et al. (2017)). LT was measured as the degree of lateral shoot growth. MH was evaluated as flower bud bunching before antithesis. MS was measured as above-ground biomass of a representative central plant. VG was evaluated as overall plant vigor. Leaf color/waxiness (LC) was evaluated visually. LA and LM were evaluated as the leaf-tip angle and degree of leaf margin serration. No intermediate flower color was detected so FC was scored as a binary trait. Other bud morphology traits (SE, SS, SF, ST, and SH) were evaluated visually as unopened buds at head maturity. The traits bud size (BS), bud uniformity (BU), bracting (BR), head compactness (HC), head diameter (HD), head uniformity (HU), head extension (HE), head shape (HS), overall-heading quality, and (OQ) were evaluated following standardized protocols developed by the Eastern Broccoli Project using an ordinal scale (1 = worst; 5 = best) with slight population specific modifications (e.g.: adjusting scale centering to account for smaller DH heads) (Stansell et al., 2017). Days to maturity and flowering (DM and DF) were calculated as days from sowing to head maturity and first flowering respectively. Holding ability HA was defined as DF–DM. Correlation matrices were computed between traits as well as between trial years by invoking the Spearman method with the cor() function in R v3.6.0(R-Core-Team, 2018). RIA of overall heading quality OQ was conducted with the R package ratervar (Stansell et al., 2017) using 1,000 bootstraps under the metric “lmg” by fitting the model:
Broccoli's high perishability and its sensitivity to negative quality changes (i.e., mass loss, ethylene induced degreening, abscission of leaves, and florets) generates quality problems during postharvest. Freshly harvested samples were stored at 5 and 21 °C after separately treated for 24 h with 625 ppb 1-methyl-cyclopropene (1-MCP), 24 h with 2 ppm ethylene and 1-MCP followed by ethylene. Quality maintenance effectivity of 1-MCP was investigated during cold and room storage by non-destructive optical methods (chlorophyll fluorescence and DA-index®) and by the evaluation of the visual physiological symptoms. The highly positive effects of 1-MCP treatment combined with cold storage were obviously proven on quality maintenance providing better retention of initial quality related to the initial mature green stage as chlorophyll content related DA-index®; Fm, Fv, Fv/Fm, and Fm/F0 chlorophyll fluorescence values. From the practical point of view, the rapid, and easy-to-use Sintéleia FRM01-F Vis/NIR DA-meter® could be applied relatively easy for the quality measurement of broccoli. The reproducibility of quality determination could be increased by the enhanced number of measuring points or using computer aided imaging methods (i.e., chlorophyll fluorescence imaging, machine vision system) providing global and more reliable information about quality changes.
Nowadays, postharvest quality issues of fresh horticultural products are continuously under the scope of interest. During the postharvest life of horticultural products, especially during cold storage, or even during ambient storage or refrigerated shelf-life, several type of losses/injury/damage occurs: chilling injury (Cen et al., 2016; Patel et al., 2016; Zsom et al., 2018); ethylene damage (Martinez-Romero et al., 2007; Watkins & Nock, 2012); mechanical injury (Li & Thomas, 2014); low O2 and/or high CO2 (Beaudry, 1999). Among vegetables, broccoli is one of the favorites of the cabbage family. Broccoli is a highly perishable vegetable. According to Cantwell and Suslow (1997), low temperature is extremely important to achieve the adequate shelf-life. Optimal temperature of 0 °C with >95% relative humidity (RH) is required to optimize broccoli storage life (21–28 days). Heads stored at 5 °C can offer a shorter storage life for a maximum of 10–14 days; but its storage life at 10 °C is only about 5 days. Ethylene can easily diffuse into and out of plant tissues from endogenous (biological) and exogenous (non-biological) sources (Saltveit, 1999). Additionally, broccoli is extremely sensitive upon exposure to ethylene from natural origin (produced by climacteric fruits) or artificial origin (i.e., from exhaust fumes of internal combustion engines). Due to ethylene exposure, yellowing (chlorophyll degradation) and abscission of the florets and leaves are the most common postharvest symptoms. Exposure to 2 ppm ethylene at 10 °C reduces the possible shelf-life by 50% (Cantwell & Suslow, 1997). Additionally, broccoli is also really sensitive to mechanical injury; high mass loss caused softening, mold development and decay among improper transportation and retail conditions. In order to avoid such losses, individual shrink packaging (film wrapping) is the commonly used procedure. Novel postharvest technologies (i.e., the use of ethylene binding packaging materials, or ethylene scavenging agents) could serve effectively for these purposes. 1-MCP (1-methyl-cyclopropene) application as a novel postharvest treatment (Blankenship & Dole, 2003) is proved to be effective against undesired postharvest ripening of several fruits such as apples, bananas, pears, plums, melons (Bagnato et al., 2003; Nguyen et al., 2016; Nguyen et al., 2018; Watkins, 2006), but the possible application for vegetables, especially for broccoli is rather rare lately (Fan & Mattheis, 2000; Fernández-Léon et al., 2013; Sabir, 2012; Toivonen & DeEll, 1998; Yuan et al., 2010). The main effect of 1-MCP is that this highly active and harmless compound is able to fit in, bind more strongly and block the ethylene receptors than ethylene, thus prolonging storage life (especially if used parallel to cold and/or controlled atmosphere storage), preventing ethylene-dependent physiological responses and providing better retail quality. According to Zsom-Muha and Felföldi (2007), the postharvest quality assessment and control is rightly waiting for the new possibilities of reliable, objective, and quantitative methods. These novel methods are also welcomed for broccoli quality determination because of its special morphology and structure derived measuring difficulties. So, the now available novel non-destructive optical measuring methods are based for example on the measurement of chlorophyll content related absorbance differences, chlorophyll fluorescence characteristics, or carried out by machine vision or hyperspectral imaging systems offering the possibility to non-invasively characterize the quality changes of perishable fruits and vegetables (Gorbe & Calatayud, 2012; Ziosi, 2008; Pinto et al., 2015).
The aim of our research was to evaluate and prove the possible positive effects of 1-MCP treatment on keeping the quality of fresh broccoli at cold and simulated shelf-life storage temperatures by non-destructive measuring methods. Additionally, the applicability of possible non-invasive measuring methods for broccoli quality changes was investigated.
Materials and methods
Fresh mature green broccoli samples (Brassica oleraceae cv. botrytis var. italica) were obtained from an experienced broccoli grower in uniform maturity within 12 h after harvest. According to uniformity, 30 broccolis were selected and randomly divided into four groups according to further treatments. Broccolis were stored in temperature controlled refrigerators at 5 ± 0.5 °C for 9 days. In case of ambient temperature of 21 ± 0.5 °C, samples were stored only for 5 days due to the fast quality degradation. Broccoli samples were wrapped in commercially available Low-density polyethylene (LDPE) bags. Fifteen equally distributed individual measuring points were selected on the head (or curd, which consists of many floral shoots) of each broccoli sample. These fifteen points were randomly selected for non-destructive chlorophyll fluorescence analysis and for DA-index® evaluation.
In three different series, the following treatments were carried out. Four-four pieces of fresh broccolis per storage temperatures were treated for 24 h with 1-MCP (625 ppb gaseous 1-MCP concentration, released from a tablet form in distilled water according to the SmartFreshSM system application requirements), 2 ppm of ethylene (C2H4) and the consecutive combination of the earlier two (24 h of 1-MCP followed by 24 h of ethylene) in an air-tight plastic cabinet equipped with a small electric fan for adequate air distribution inside the cabinet, respectively.
Mass loss (% of fresh mass) was calculated based on the measured mass data using a digital laboratory balance for each sample on every measuring day.