GARLIC QUALITY TESTING
Phenotypic characterization and quality traits of Greek garlic (Allium sativum L.) germplasm cultivated at two different locations
In the present study, we examined the phenotypic diversity of Greek garlic (Allium sativum L.) genotypes using morphological descriptors derived from IPGRI and UPOV. Thirty-four garlic genotypes were cultivated at two different locations: (a) Velestino, Magnesia, Region of Thessaly, and (b) Kavasila, Ilia, Region of Western Greece. The garlic genotypes were characterized using twenty-seven morphological descriptors and four quantitative characters, namely bulb dry matter, chlorophyll content in the leaf, yield and total soluble solids (°Brix) of plants and raw bulbs. The Shannon–Weaver (H′) phenotypic diversity index varied among the genotypes, although identical mean values (0.79) were recorded for both fields. Traits, such as flowering stem length, bulb skin color, skin color of the clove presented low (H′) values indicating a high coefficient of heritability and less environmental effect. Principal component analysis based on morphological characters showed that the first seven axes could explain 71.49% and 75.86% of total variation for Kavasila and Velestino fields respectively. Significant differences were also observed among the garlic genotypes for the quantitative characters studied. Furthermore, significant statistical correlations were recorded for specific characters between the two cultivation sites e.g. yield with weight of cloves (r = 0.55 and r = 0.62) and number of cloves per bulb with weight of cloves (r = −0.51 and r = −0.55), which could be exploited further in future breeding programs. In conclusion, the high phenotypic diversity observed among the garlic genotypes could be attributed to various factors such as the genotype, the cultivation practices and the environmental conditions.
Grades of Garlic
U.S. No. 1 consists of garlic of similar varietal characteristics which is mature and well cured, compact, with cloves well filled and fairly plump, free from mold, decay, shattered cloves, and from damage caused by dirt or staining, sunburn, sunscald, cuts, sprouts, tops, roots, disease, insects, or mechanical or other means. Each bulb shall be fairly well enclosed in its outer sheath. Unless otherwise specified, the minimum diameter of each bulb shall be not less than 1-1/2 inches.
a. Tolerances. In order to allow for variations incident to proper grading and handling, the following tolerances, by weight, are provided as specified:
1. For defects. Ten percent for garlic in any lot which fails to meet the requirements of this grade, including therein not more than 2 percent for garlic which is affected by decay.
2. For size. Five percent for garlic in any lot which fails to meet any specified size.
GARLIC QUALITY MANAGEMENT SOLUTION
Garlic-specialized metabolites contribute to both spicy flavor and healthy function of garlic. Their accumulation pattern and regulatory mechanism vary greatly at different environments and maturities. Herein, metabolomics models were built to evaluate and predict the quality and chemical composition variances of four garlic varieties in two regions at six growth stages. A total of 91 metabolites were identified, and their accumulation pattern during growth in three varieties of garlic in Shandong was similar but obviously distinct from that planted in Heilongjiang. Active metabolism for organosulfur compounds and amino acids was observed, and most metabolites with the “γ-glutamyl-” group were the storage compounds of nitrogen and sulfur in garlic because they increased remarkably during growth. The levels of functional components in garlic varied among different stages, and reliable prediction models for these compounds were provided, which may give a new idea for the estimation of garlic quality and confirmation of the best harvest time.
KEYWORDS:garlic bulb growth stage metabolomics pathway prediction model
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jafc.0c01120.
Identification of main chemical constituents in garlic by UHPLC Q-Exactive Orbitrap MS (Table S1), detailed websites from MoNA that support the identification of 12 compounds in garlic (Table S2), contents of 29 targeted compounds in garlic among different growing stages (Table S3), agro-morphological traits of garlic in different growing stages (Table S4), parameters of OPLS regression models for characteristic components in garlic based on agro-morphological traits (Table S5), observed and predicted concentrations and RE between them for the testing set predicted by OPLS regression models (Table S6), VIP values for agro-morphological traits in OPLS regression models for allicin and a total of seven flavor precursors in ZP, J3, J4, and BP (Table S7), workflows and parameters of Compound Discovery 3.0 analysis (Figure S1), MS/MS spectra of 29 compounds identified in the garlic sample and mzCloud (Figure S2), structural characterization for 13 compounds in garlic (Figure S3), TIC obtained by UHPLC Q-Exactive Orbitrap MS of extracts from garlic bulbs of ZP, BP, J3, and J4 at weeks 1, 4, and 6 (Figure S4), and pathway analysis showing changing metabolism during garlic development (Figure S5) (PDF)
GARLIC QUALITY MANAGEMENT
ARLIC QUALITY AS A FUNCTION OF SEED CLOVE HEALTH AND SIZE AND SPACING BETWEEN PLANTS
Garlic has a worldwide economic importance; this vegetable can be consumed fresh or processed by food industries. However, few studies evaluate its postharvest quality. It is necessary to establish cultural practices and methods that focus not only on increase of yield, but on obtaining a product with better postharvest quality. The objective of this work was to evaluate the bulb quality of conventional garlic and virus-free garlic as a function of seed clove size and space between plants. Two experiments were conducted simultaneously in Portalegre, Rio Grande do Norte, Brazil. A randomized block experimental design with four replications was used in both experiments. The treatments were arranged in split-plots, with the seed clove size (large and small) in the plots, and the plant spacings (7.5, 10.0, 12.5, and 15.0 cm between plants) in the subplots. The use of large seed cloves resulted in higher bulb diameter and titratable acidity (TA). Soluble solids (SS), total soluble sugars, SS to TA ratio, and total solids decreased as the space between plants was increased, regardless of the seed health and seed clove size. Virus-free garlic seed cloves planted with spacing of 12.5 and 15.0 cm resulted in higher bulb diameter, TA, pungency, and industrial index, i.e., they produced better quality bulbs with good prospects for industrialization.
Allium sativum L; Soluble solids; Pungency; Industrial index
Garlic is a well-appreciated vegetable worldwide due to its flavor, aroma, spice, and medicinal properties (OLIVEIRA et al., 2010).
Most garlic in Brazil is marketed fresh, but in recent years, it has been used in industrialized products that are well accepted by consumers, such as garlic paste and dehydrated garlic, adding value to this product.
The adoption of new technologies for garlic production is important because of the increasing demand of the food market, including virus-free garlic seeds and cultural practices for the field phase, which can enable garlic to reach the market with better quality for the consumers.
The use of virus-free garlic seeds has resulted in plants with greater vigor, mainly due to the absence of degenerations caused by viruses. Consequently, these plants have greater bulb yield than those from conventional seeds, and bulbs with better quality and good prospects for food industries, adding value to the product (RESENDE et al., 2013).
Determining the bulb pungency is important for the analysis of garlic quality; it depends on the concentration of pyruvic acid, which is responsible for the characteristic garlic flavor and aroma. Bulbs with high concentration of pyruvic acid are desirable because it is responsible for the industrial yield (industrial index); this is essential for choosing the raw material for processing, because the higher this concentration the higher the pungency of the flavor and aroma of the final product, which are characteristics desired by consumers (VARGAS et al., 2010; LUCENA et al., 2016).
Other factors of crop management can improve bulb quality, such as the space between plants and the seed clove size used for planting. Some researchers have reported the effect of plant population and seed clove size on postharvest conservation and commercial quality of garlic bulbs, indicating the most appropriate processing and dehydration treatments for the industry.
According to Randle (1997), chemical composition and sensory characteristics of flavor and aroma depend more on genetic factors than on crop conditions, but the bulb chemical composition and flavor intensity are also dependent on plant development conditions and also on crop management practices, such as planting density and seed clove size.
Studies in several garlic producing regions in Brazil have evaluated garlic plant growth and yield as a function of plant population and seed clove size. However, few of them consider the postharvest quality, which is important for choosing cultivars, crop managements, and the acceptance by the consumer market. Thus, the objective of this work was to evaluate the bulb quality of conventional garlic and virus-free garlic as a function of seed clove size and plant spacing.
MATERIAL AND METHODS
Two experiments were conducted, one with conventional garlic seed cloves (infected with virus), and other with virus-free garlic seed cloves obtained from the Brazilian Agricultural Research Corporation (EMBRAPA). The experiments were carried out simultaneously from May to September 2017, in Portalegre, state of Rio Grande do Norte, Brazil (6°1'20"S, 38°1'45"W, 520 m altitude). According to the Köppen classification, the region has an Aw, tropical rainy climate, with a dry winter, a rainy season extending to July, and an annual average rainfall depth of 800 to 1,200 mm. The air temperature was monitored during the experiment, showing averages of 15 to 21 °C (minimum), 24.7 °C (average), and 26 to 34 °C (maximum).
The soil of the area where the garlic was produced was classified as a eutrophic Neossolo Litolico of weak A horizon and a medium texture (EMBRAPA, 2018). The chemical analysis of the soil showed pH (H2O) of 4.60, 4.97 g Kg-1 of organic matter, 0.07 g kg-1 of N, 5.3 mg dm-3 of P, 79.7 mg dm-3 of K, 8.9 mg dm-3 of Na, 2.6 cmol dm-3 of Ca, 1.3 cmol dm-3 of Mg, 0.1 cmol dm-3 of Al, and base saturation of 64%.
The experiments were conducted in a randomized block design with four replications. The treatments were arranged in split plots. The plots consisted of bulb sizes: large [bulbs retained in sieves 1 (15×25 mm) and 2 (10×20 mm)]; and small [bulbs retained in sieves 3 (8×17 mm) and 4 (5×17 mm)]. The subplots consisted of spacings between plants: 7.5, 10, 12.5, and 15 cm between plants, with 20 cm between rows, corresponding to planting densities of 500, 375, 300, and 250 thousand plants per hectare, respectively.
The virus-free garlic seed cloves had average weights of 1.51 to 2.32 g (large size) and 0.83 to 0.98 g (small size); and the conventional garlic seed cloves had average weights of 1.87 to 2.61 g (large size) and 0.91 to 1.28 g (small size).
The garlic cultivar used was the Roxo Pérola de Caçador. The garlic clove seeds underwent a vernalization process for 50 days in a cold chamber at 4±2 °C and relative humidity of approximately 70%. The bulbs were withdrawn from the cold chamber at one day before planting for threshing and, then, they were classified by size, according to Regina and Rodrigues (1970), and planted according to the treatments.
The subplots consisted of beds with height of 0.2 m, width of 1.0 m, and lengths of 1.50, 2.00, 2.50 or 3.00 m, according to the spaces between plants of the treatments (7.5, 10, 12.5, and 15 cm), with five planting rows, totaling 100 plants. The evaluation area of the subplots consisted of the three central rows, discarding one plant at each end of the rows, resulting in a population of 54 plants.
The soil preparation consisted of a plowing and harrowing, followed by the formation of the beds. Then, the soil acidity of the beds was corrected by uniformly incorporating 400 kg ha-1 of Ca(OH)2. Fertilization at planting was based on the soil chemical analysis and recommendations of Cavalcanti (2008), using 30 kg ha-1 of N (calcium nitrate), 180 kg ha-1 of P2O5 (simple superphosphate), 60 kg ha-1 of K2O (potassium chloride), 15 kg ha-1 of Mg (magnesium sulphate), 12 kg ha-1 of Zn (zinc sulphate), 1.7 kg ha-1 of B (boric acid), and 40 Mg ha-1 of a beef and chicken manure fertilizer (Pole Fértil®) containing 1% N and 15% organic C, with 50% moisture, pH of 6.0, and CEC of 80 mmolc dm-3.
Topdressing was performed at 20 and 50 days after planting, using 30 and 60 kg ha-1 of N with calcium nitrate and urea, respectively.
Weed control was carried out manually, maintaining the plants in a weed-free environment. Phytosanitary control was performed using mancozeb-based products to control purple spot. The control of pest, such as thrips and mites, was carried out using clorfenapir-based products.
Irrigation was performed using a micro sprinkler system, with flow of 40 L h-1, pressure of 200 KPa, and micro sprinklers spaced 1.0 m long in the subplots. Irrigation was suspended three days before harvest, when the plants presented signs of maturation-yellowing and partial drying of the aerial part. Harvesting was performed manually and the plants were subjected to a pre-cure process, remaining for three days exposed to the sun, and to a cure process, in which they remained for 17 days in a shaded, dry, ventilated place. Subsequently, the bulbs were cleaned and processed.
The diameters were measured using a sample consisted of 10 bulbs per subplot. These bulbs were then threshed, and their cloves were manually peeled, ground in a food processor, and analyzed for the following characteristics:
bulb diameter (mm): average of the cross-sectional diameters of 10 bulbs of each subplot;
soluble solids (%): determined directly from the homogenized garlic juice, which was filtered on a polyester fabric and read on a digital refractometer (Palette PR-100, Atago, Saitama, Japan); the results were expressed as percentages (AOAC, 2002);
total soluble sugars: quantified by the Antrona method, described by Yemm and Willis (1954); 0.2 g of garlic paste was diluted in distilled water in a volumetric flask to a volume of 100 mL and filtered to obtain the extract; 50 µL of the extract and 950 µL of distilled water were added to a test tube, which was subjected to an ice bath, while the Antrona solutions (2 mL) was added. The test tubes were then shaken and immediately returned to the ice bath and, subsequently, they were boiled over a water bath for eight minutes. Then, they were cooled on ice water. The standard curve was developed using glucose solution at concentrations of 0, 10, 20, 30, 40, and 50 mg L-1. The solutions were read in a spectrophotometer at 620 nm and the results were expressed in g 100 g-1 (%);
titratable acidity: 1 g of garlic paste was diluted in distilled water to a volume of 50 ml. Two drops of 1% alcoholic phenolphthalein were added. Titration was performed with 0.1 N NaOH solution to the turning point characterized by the pink color. Results were expressed as mEq H3O+ 100 g-1 (IAL, 2005);
Soluble solids to titratable acidity ratio.
Pungency: estimated by determining the pyruvic acid content using 2,4-dinitrophenylhydrazine reagent (DNPH), by the colorimeter method (SCHWIMMER; WESTON, 1961). An aliquot of 0.2 mL of garlic juice was placed in an Erlenmeyer flask, and 1.5 mL of 5% trichloroacetic acid and 18.3 mL of distilled water were added to obtain the extract. The solution was stirred and, then, 1 mL of the extract, 1 mL of 2,4-dinitrophenylhydrazine (DNPH) solution, and 1 mL of distilled water were added to a test tube. The solution was vortexed and the test tubes were placed in a water bath at 37 °C for 10 minutes. The solution was cooled in an ice bath and 5 mL of 0.6 N NaOH was added in each test tube. They were vortexed and left to rest for five minutes to develop a yellow color. Absorbances were read on a spectrophotometer at 420 nm. Sodium pyruvate was used as standard. The pungency was calculated by drawing the standard sodium pyruvate curve at seven concentrations (0.0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mmol L-1). The results were expressed in µMoles of pyruvic acid per mL of garlic juice;
total solids: seed cloves of a sample of ten bulbs were taken to a forced air-circulation oven at 65 °C until constant weight. The total solids were calculated by the difference between 100 and the moisture content of the seed cloves; the results were expressed as g of total solids per 100 g of garlic (%) (IAL, 2005);
Industrial index: calculated by the formula Industrial index = (total solids × pyruvic acid) 100-1, according to Carvalho et al. (1991).
The data were subjected to analysis of variance for each experiment separately. Observing the assumptions for homogeneity of variances and normality of errors between experiments, the data were subjected to joint variance analysis; the means related to bulb size and seed health were compared by the t test (p=0.05); and the means related to plant spacing were compared by regression analysis and the F test (p=0.05).
RESULTS AND DISCUSSION
The interaction between plant spacing and seed health was significant for bulb diameter. Seed health had significant effect on titratable acidity (TA), soluble solids to titratable acidity (SS to TA) ratio, pungency, total solids, and industrial index. Seed clove size had significant effect on TA, SS to TA ratio, and bulb diameter. Space between plants had significant effect on TA, SS, SS to TA ratio, total soluble sugars, pungency, total solids, and industrial index.
The bulb diameter (BD) of garlic plants from large seed cloves was higher than that of those from small seed cloves (Table 1). This is because plants from large seed cloves can have higher leaf area index than those from smaller ones, resulting in higher accumulation of photoassimilates and higher BD (CASTELLANOS et al., 2004). The higher carbohydrate and mineral reserves in large bulbs produce vigorous plants that establish faster and have better development when compared to those from smaller bulbs (LENCHA; BUKE, 2017). Similarly, Mahadeen (2011) reported that the seed cloves with lower weights affected bulb length and diameter.
Average values of bulb diameter, titratable acidity, and soluble solids to titratable acidity ratio (SS/TA) of garlic as a function of seed clove size.
The garlic seed health affected the BD; the plants from virus-free seeds had higher BD than the those from conventional seed in all the evaluated spacings between plants, with most bulbs in classes 4 (> 37 to 42 mm) and 5 (> 42 to 47 mm) (Table 2). This difference due to seed health is explained by the higher vigor of plants from virus-free seeds, higher plant height and number of leaves (data not shown), and, probably, higher net assimilation rate, which resulted in bulbs of larger transverse diameter. According to Henriques (2016), the increase in BD is related to the number and length of leaves and plant height, thus, plants with larger leaf area have higher production and translocation of photoassimilates for bulb growth.
Average values of noble garlic bulb diameter as a function of garlic seed health in each space between plants evaluated.
Similarly, Resende et al. (2000) found higher bulb size with virus-free garlic cultivars. According to Marodin (2014), the use of virus-free garlic seeds results in 100% more large bulbs (diameter greater than 52 mm) when compared to plants from conventional seeds; and the use of conventional garlic seeds results in a higher production of non-commercial bulbs (diameters lower than 32 mm).
The BD of both garlic seeds (conventional and virus-free) increased as the planting spacing was increased, reaching BD of 38.73 (conventional) and 45.65 mm (virus-free) in the spacing of 15.0 cm between plants (Figure 1).
Bulb diameter of garlic from conventional (CON) and virus-free (VF) seeds as a function of spacing between plants.
Increases in BD due to lower plant densities was reported in other studies (AHMED et al., 2017; MUNEER et al., 2017). Lower plant densities result in greater sunlight incidence, higher photosynthetic rates, and lower competition between plants for nutrients and water, generating greater vegetative growth and bulbs with larger diameters (MORAVČEVIĆ et al., 2011).
Mengesha and Tesfaye (2015) found similar results for garlic plants of the Chiro cultivar (Ethiopian variety) grown with spacings of 10, 15, and 20 cm between plants and 30 cm between rows; they found increases in BD as the spacing was increased: the largest BD (34.59 mm) was found with the spacing of 20 cm and the lower BD (30.44 mm) with the spacing of 10 cm. However, Doro (2012) compared four spacings between plants (5, 10, 15, and 20 cm) and found no variation in BD between the spacings of 10 and 15 cm, while the spacing of 20 cm resulted in greater BD when compared to the spacings of 5 and 10 cm.
According to the results of soluble solids (SS) content as a function of spacing between plants, the highest SS was found in the spacing o
GARLIC QUALITY SYSTEM
Fruits and vegetables are the staple sources of antioxidants. The antioxidant properties may wear off with time. The present study was aimed to investigate and compare the antioxidant capacity of aged garlic (three-month old) with that of the fresh (newly harvested) garlic. In the present interventional study, an ethanol extract was obtained from fresh and aged cloves of garlic and their antioxidant capacity were measured in linoleic and β β β β-carotene linoleate models. Phenol compounds were assayed using Folin-Ciocalteu colorimetry equivalent to Gallic acid and the flavonoid and flavonol compounds were assayed utilizing chloride aluminum colorimetry method equivalent to rutin. The allicin level was measured through spectrophotometry. Fresh garlic was more efficacious (35.63) than the three-month old garlic (10.2) in inhibiting oxidation. In the linoleic acid and β β β β-carotene linoleate models, no significant difference was found between the fresh garlic and old garlic extracts in terms of optical density (p>0.05). The phenol compounds in the fresh garlic (12.61mg/g) were higher than those of the three-month old garlic (2.89 mg/g). Allicin level in the fresh garlic extract (15 µg/ml) was shown to be higher than three-month old garlic extract (8 µg/ml). The results of the present study suggest that garlic should be preferably consumed fresh as it maintains its beneficial compounds.