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Improving Avocado Quality

Dr. Vijayalaxmi Kinhal

December 5, 2022 at 6:27 pm | Updated December 22, 2022 at 11:43 pm | 12 min read

Quality avocados must be safe for consumption and satisfy consumer preferences like appearance and taste.  

  • Dry matter content is crucial in estimating maturity, storage, and transport conditions, ripening duration, oil content, and consumer satisfaction. 
  • Management during the production and postharvest stages is crucial to meet consumer preferences for avocados. 
  • Avocados of different qualities can be used for various purposes, monitoring quality can help better allocate a crop and avoid waste.  

Why People Want Avocadoes 

Avocado is a specialty crop that originated from south-central Mexico to Guatemala.  

Demand for fruit has been rising over the past two decades, and there is significant international export to the US and Europe from tropical countries. People consume avocado plain or prepared into guacamole, smoothies, and desserts. Besides food, avocados are also used in the cosmetics and medical industries. 

The health benefits of avocados have also been driving the demand for this fruit. Avocado provides healthy fats, protein, folate, potassium, and vitamins (C, B5, B6, E, and K). Most carbohydrates are fibers, so the produce is suitable for dieting and increasing gut flora. The American Heart Association promotes moderate consumption of avocados since it has mono and polyunsaturated fats that can replace food rich in saturated or Trans fats. Moderate consumption can decrease blood cholesterol and reduce heart disease risks. 

A year-round supply of avocados is possible since the produce matures at various times of the year around the globe.   

Global Avocado Production 

The avocado market was worth USD 20483.23 million in 2021 and is expected to increase by a CAGR of 5.08% to reach USD 27581.72 million by 2027. 

Mexico was the largest fruit producer, growing nearly 2.4 million metric tons in 2021, accounting for 30% of the world’s production. This is a 3% increase Y-o-Y, with Hass avocado forming 97% of the output. 

Other significant producers are Peru, Chile, California, and Colombia. 

Mexico and the USA are the major consumers of avocados. However, the USA doesn’t produce enough and has emerged as the leading fruit importer. The country imported USD 3.14 billion worth of avocados. Mexican imports meet 80%, and California meets 15% of the US demand for avocados. 

France and Spain importing avocados worth USD 538.75 million and USD 488 million are the second and third largest importers, respectively. Germany, the U.K., Canada, Japan, Russia, Chile, and China are the other top importers. 

Mexico is avocados’ largest exporter, but its production is falling by 8% in the 2021-2022 season compared to the previous season, causing prices to rise to a 24-year high in the US. 

The demand for avocado has increased after the pandemic due to its health benefits, raising its prices in combination with lower supplies. 

Fruit Biology 

The avocado fruit is a berry with a single large seed. The trees are capable of partial self-pollination, and the cultivars are of two types: A-type and B-type.  

  • A-type cultivars have flowers that function as females in the morning when they receive pollen. In the afternoon, flowers act as males and shed pollen. Hass, Choquette, Lula, Reed, Pinkerton, Gwen, and Maluma are A-type avocados.  
  • B-type cultivars‘ flowers act as males in the morning and females in the afternoon. Ettinger, Sharwil, Zutano, Brogden, Fuerte, Cleopatra, Bacon, and Monroe are examples of B-type cultivars. 

Trees are propagated by grafting to sustain the quality and quantity of yields.  

Quality Parameters and Monitoring Methods 

Figure 1: The typical colors of ripe avocados, University of California. (Image credits: http://ucavo.ucr.edu/General/FruitColor.html) 

Several studies have shown that consumers in the USA and Europe, the major destinations for avocados, consider quality and price when buying fruit. Therefore, in terms of quality, ripeness and appearance influenced people’s buying behavior.  

Appearance is the traditional means of judging quality in the supply, and consumers invariably use it while selecting food. For example, people want avocados that have developed the right color and have no external or internal discoloration.  

Externally, avocado skin color depends on the variety and can vary from green, dark green, and purple to black when ripe. Therefore, external color can’t be used in quality control of green skin avocados. However, internal color can be used in all avocados. 

Consumers judged ripeness by firmness when purchasing, see Figure 2. Producers and suppliers can use a penetrometer to evaluate avocados’ firmness before selling, but it is a destructive method, and the fruit examined has to be discarded.  

 

Figure 2: “Biplot of sensory evaluation of different ready-to-eat avocado varieties, in dimensions 1 and 2. Texture attributes were the most discriminatory, as shown by the higher variance explained by the attribute firmness and creaminess,” Giuggioli et al. (2021). (Image credits: https://doi.org/10.1155/2021/6621449) 

Loss of firmness occurs during ripening as the fruit loses moisture content, which is inversely related to dry matter. Loss of water is replaced by oil in avocados. Nearly eight decades ago, it was shown that avocados’ eating quality depended on the fruit’s oil content. The creamy, buttery taste consumers want in avocados results from the fat content. As the fruits ripen and the amount of oil rises, it can be measured by the accompanying increase in dry matter

The dry matter has become the essential quality parameter for avocados, as it indirectly predicts the amount of oil content. Nowadays, it is possible to easily estimate oil content based on dry matter through Near Infrared spectroscopy. For example, the Felix Instruments Applied food Science’s F-751 Avocado Quality Meter can accurately measure dry matter within a few seconds on the field and is used in the entire supply chain. Such tools replace earlier methods that were difficult and time-consuming to estimate oil content and eating quality, resulting in a lot of avocado wastage.  

Dry matter (DM) is also used as the maturity index. DM at harvest was proven to correlate with consumer preference. Consumers prefer avocados harvested in the range of 22–27% and firmness of 6.5 N. Fruits with less than 20% DM didn’t meet consumer taste. 

The harvest time is fixed on well-known dry matter levels for different cultivars to ensure optimal shelf life and postharvest quality of avocados, see Table 1. However, the same cultivar grown in different regions of the globe will have to be harvested at other DM contents.  

Table 1: “The minimum percent dry matter standard that various avocado varieties must reach before they can be commercially harvested and sold to the public,” International Tropical Fruits Network. (Credits: https://www.itfnet.org/v1/2016/05/avocado-post-harvest-processing/) 

Avocado quality at harvest can determine several postharvest aspects of the fruits, like storage potential, shelf-life, risk of chilling, and ripening physiology. Hence quality control of fruits must start one month before minimum maturity is reached. 

Storage & Transport Conditions 

Once harvested, avocados must be moved quickly to packing houses to reduce moisture loss. 

Packing House: At the packing house, the fruits are cleaned, graded, packed, and stacked depending on the packing house protocol and market requirements, as shown in Figure 3. 

Since dry matter content will play an essential role at several critical points in decision-making, the parameter should be estimated latest at packing houses so that fruits of the same DM content are packed together. Otherwise, a package with mixed ripening will reach retailers, leading to wastage. 

Cooling: Before transport, the fruits have to be also cooled. The temperature depends on dry matter content, distance to destination, storage requirement, and picking time (early or late season).  

Based on dry matter content, these are the following recommendations in the American market for cooling avocados:  

  • For DM content < 23% transport avocados at 7°C (or 45°F). 
  • For DM content 23-26% use 5.5°C (or 42°F). 
  • For DM content >26%, cool to 4.5°C (or 40°F), and for fruits approaching 30% DM, cool to 3.9°C (or 39°F) 

Late-season avocados with high DM content must be shipped at 3.3°C (or 38°F). Fruits with less DM should not be transported at temperatures lower than recommended, as it can cause chilling injury. Care should be taken during loading to maintain recommended cooling temperatures. 

Storage: Distribution Centers are responsible for holding the avocados at the recommended cooling temperatures after transport. Fruits should be removed from cold storage only close to repacking time. 

Avocados are more perishable than other produce. It is usually stored for only four weeks, and extending the shelf life to six weeks can be challenging. Storage rooms must be checked for gas buildup from respiration once a week. Ethylene levels must be checked only for fruits at later maturity stages and after prolonged storage.  

Undertake ethylene scrubbing if necessary. Once ethylene-induced ripening has started, avocados have a short shelf life and become susceptible to infections, chilling injury, and rot. In addition, since avocados are highly sensitive to ethylene, they should not be stored with climacteric ethylene producers like apples, bananas, nectarine, etc. 

Felix Instruments Applied Science has several gas analysis tools for various supply chain stages to measure the three gases- carbon dioxide, oxygen, and ethylene nondestructively and precisely. 

Figure 3: Avocado treatment in a packing house, Bower. (Image credits: https://hassavocadoboard.com/wp-content/uploads/Hass-Avocado-Board-Quality-Manual.pdf)  

Ripening: Green hard fruits must be ripened to be ready to eat before retailing. However, they should only be allowed to ripen partially, as this can shorten their shelf life unless they are meant for food service or processing.  

Usually, avocados are ripened in ethylene ripening rooms. If ripened outside ripening rooms, use 20-22°C (68 to 72°F). 

The time avocados need to reach a ready-to-eat stage depends on the cultivar, temperature, maturity stage at harvest, and region of origin. Therefore ripening must be conducted in uniform batches. 

Avocados are ripened using a catalytic generator in artificial ripening rooms. Though there are many ripening agents on the market, these are forbidden. Instead, ethylene, a natural phytohormone, is used at concentrations varying from 10 to 1000 ppm and at a temperature of 15.5°C and relative humidity of 90-95%. Every eight hours, the room should be vented for 30 minutes to remove carbon dioxide. These levels should preferably be less than 1%.  

The exposure time to ethylene depends on maturity or dry matter content: 

  • Avocados with a DM of <23% must be ripened for 2 to 3 days. 
  • Fruits with DM of 23-26% need 1 to 2 days. 
  • Avocados with DM >26% need one day. 

After ripening, fruits are repacked and kept at 5-6.6°C (41 to 44°F) until dispatch. 

Best Practices– Preharvest and postharvest 

Several best practices to increase and maintain avocado quality concern dry matter content at harvest.  

Figure 4: “The distribution of dry matter (DM) percentage in individual ‘Hass’ avocados from each maturity category. The median DM for each category was 20%, 22%, 26% and 38% for 

‘immature,’ ‘early’, ‘mid’ and ‘late’ maturity categories,” Gamble et al. 2010. (Image credits: doi:10.1016/j.postharvbio.2010.01.001). 

  1. Avocado has a unique ripening method, where fruits only ripen after being harvested. So fruits can remain on the tree for 12 months after reaching physiological maturity. During this time, fruits continue to accumulate dry matter, see Figure 4. Producers use this feature of avocado to manipulate horticultural maturity by delaying harvesting till late in the season or until the demand for the fruit is high. Early-season fruits have little demand as they have less DM content and ripen unevenly. Consumer acceptance improves with a delay in harvest date; see Figure 5. 

Figure 5: “Consumer scores for liking (A) and purchase intent (B) for ‘Hass’ avocados from the different maturity categories: immature (median = 20% DM); early (22% DM); mid 

(26% DM) and late (38% DM),” Gamble et al. 2010. (Image credits: doi:10.1016/j.postharvbio.2010.01.001) 

  1. Stop irrigation one day before harvest to prevent fruits from getting turgid and suffering from lenticel damage during plucking and transport.
  2. Scorching days for harvest should also be avoided since the higher rate of water loss and respiration will continue after plucking and reduce shelf life. 
  3. Conditions during the growing season affect fruit composition in the pulp and skin and influence ripening processes. For example, fruits suffering from trees or areas with calcium deficiency will ripen faster and have more ethylene respiration. These fruits should be sorted for immediate marketing and sent to nearby regions. 
  4. Postharvest treatment to prolong shelf life includes temperature management and the application of edible coatings of 1-methylcyclopropene (1-MCP). 
  5. Fruits should be stored for at most 24 hours in packing houses before cooling. 
  6. To ensure a successful coordinated quality management program throughout the supply chain, packing houses should include documentation on cooling requirements, dry matter content, and maturity stages of packages and batches. 
  7. The stage of maturity at harvest time and the temperature affect the rate of avocados ripening. Therefore, ripen the fruits slowly at recommended temperatures and time. Trying to hasten the process with higher temperatures can lead to improper ripening and physiological disorders. 
  8. Use only ethylene; other cheaper ripening agents can have short-term and long-term adverse health effects. Calcium carbide ripened fruits cause stomach problems for consumers and are associated with occupational hazards like permanent skin damage, vomiting, etc. Ethylene glycol can cause kidney damage to consumers. 

Regulatory and Industry Support Organizations 

The primary regulatory organization in the USA is the Hass Avocado Board (HAB). The two-decade-old organization collects and distributes investments to promote the global avocado trade. It aims to make the fruit popular in the country and sets standards and protocols for harvesting, storing, and ripening avocados from different countries. 

In addition, the HAB conducts nutrition research and provides the industry with market and supply data. It also helps bring stakeholders from around the globe. 

HAB has set specific transport and storage requirements for each country from which it imports avocados. For example, Peru ships the fruits in containers having a controlled atmosphere. The levels of oxygen and carbon dioxide will differ depending on the companies. Some use 5% O2 and CO2, others 4% O2 and 6% CO2, etc.  

The other major consumer and producer of avocados, Mexico has the Association of Avocado Exporting Producers and Packers of Mexico (APEAM) to guide the avocado industry in the country. A non-profit, APEAM represents 30,000 growers and 34 packing houses. It is the only organization cleared to export the fruit to the USA.   

APEAM plays a crucial role in the success of Mexican avocado export to the USA and several other regions like Europe, Japan, China, etc. It ensures that avocados are traceable, safe, and sustainable. APEAM also promotes transparency, efficiency, and accountability. It has been instrumental in improving growers’ economics and protecting workers’ rights. APEAM has been active in creating jobs and cutting undocumented emigration from the Michoacan state to the USA 

Maturity Requirements Thresholds 

Countries exporting avocados to the USA follow the recommendations by HAB for domestic production. So all exporters ensure that the minimum dry matter at harvest is above 20.8% for ‘Hass.’ 

Several countries require that their avocados have a higher DM content of ∼25% so that they can withstand long-distance transport and storage better without suffering from disorders 

Processing Avocadoes 

Avocados are eaten fresh or processed to make baked products, soup mixes, appetizers, and cosmetics such as oils, soaps, skin lotions, shampoos, etc. 

Avocado pulp has 60% oil, and the oil extracted is widely exported.  

  • “Extra virgin” oil is extracted from avocados of good quality only with mechanical means at temperatures below 50°C.  
  • “Virgin” avocado oil is produced from fruits of lower quality with some rot or bruising. 
  • “Pure” oil is produced from avocados, and quality is not essential. 

Avocados that are unsuitable for eating fresh can be used to make oil. So adequate quality control in the supply chain to sort fruits for fresh consumption or oil extraction can reduce crop loss. Growing and environmental conditions influence the fatty acid profile, not postharvest ripening conditions. Maturity stages are crucial, and as fruits ripen, the amount of oil extracted can increase.   

Avocado oil is used for consumption because of its unsaturated fatty acids, vitamins, and antioxidant content. Though avocado pulp quality is well documented, there is little known about the quality of avocado oil and its health implications. Avocado oil can also be used to produce biodegradable polymers and cosmetics. In addition, there are efforts to find other industrial applications like the production of structured lipids or improving natural emulsifiers. 

Other essential avocado-processed products are sauces, drinks, and guacamole. The fruit is cleaned, peeled, cut, and deseeded. The pulp is then used for various food preparations. 

Quality Control 

Avocado cultivation has a negative environmental impact, as a single avocado requires nearly 70 liters of water per fruit and produces 400 gm of carbon emissions. In addition, tropical forests are being cut to meet international demands, and the production is connected with social concerns. Hence it is necessary to see that none of this popular but contentious crop is wasted. One way of achieving this is through proper quality control to avoid loss and waste.   

Sources 

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