Fruit maturity and quality Azra Alikadić Web Valley 2016, San Lorenzo Dorsino
Quality - Quality implies the degree of excellence of a product or its suitability for a particular use. - Which combines: i) sensory properties (appearance, texture, taste and aroma), ii) nutritive values, iii) chemical constituents, iv) mechanical properties, v) functional properties and vi) defects. - Quality is a combination of product and consumer orientation. - Agricultural supply chain is very long, and every next step taken can be considered as a consumer: GROWER -> packer -> distribution and/or wholesaler -> retailer -> produce manager -> shelf stocker -> shopper -> the ultimate CONSUMER who eats the product.
Quality - Measurement of quality: What? How? Values? are determined by the person or institution requiring the measurement. Depends on the i) intended use of the product, ii) available technology, iii) economics and iv) often tradition. - People use all of their senses to evaluate quality: sight, smell, taste, touch and even hearing. The consumer integrates all of those sensory inputs appearance, aroma, flavour, hand-feel, mouth-feel and chewing sounds - into a final judgment of the acceptability of that fruit or vegetable. - Instrumental measurements are preferred over sensory evaluations for many researcher and commercial applications: instruments reduce variations among individuals and and can provide a common language among researchers, industry and consumers.
Quality - Fruits and vegetables are notoriously variable, and the quality of individual pieces may differ greatly from the average. - It is essential to determine statistically the number of pieces and the number of measurements per piece required to achieve significant, representative sampling. - Quality and Maturation/Ripeness: to achieve an ideal quality you harvest at an ideal maturation. So often empirical methods developed to measure some particular quality attribute actually measure ripeness e.g. color.
Measuring Quality and Maturation - In the recent years consumers have become more aware of quality and have greater expectations. How to measure fruits internal and external attributes, nondestructively and rapidly has become more important.
Precision farming - The biggest revolution in agriculture happened when machinery replaced horses with tractors. - Today, new change is happening by the adoption of new technologies: satellites, high precision positioning systems, smart sensors and a range of IT applications combined with high-tech engineering. All aspects of the environment - soil, weather, vegetation, water - vary from place to place. By being able to manage these variations in the field accurately you can grow more food using fewer resources and reduce production costs.
1 / 3 of food produced is wasted = 1.3 billion tonnes Every year, consumers in rich countries waste almost as much food (222 million tonnes) as the entire net food production of subsaharan Africa (230 million tonnes).
Precision farming - A farmer needs to formulate an effective growing strategy (1) which conditions are relatively stable during the growing season; (2) which conditions change continually throughout the growing season; and (3) information to diagnose why their crop is thriving in some parts of the field and struggling, or even dying, in other parts. - A number of scientific studies over the last 25 years have shown that measurements in visible, near-infrared, thermal infrared, and microwave wavelengths of light can indicate when crops are under stress. Farmers no longer must treat a field of crops as one homogeneous unit e.g for pesticide use, harvest, consumer quality requirements, etc.
Case Study: Grape Maturity for Quality Wine
Grape Maturity - Following flowering there are three stages of berry development: 1) Green berry growth, 2) Arrest of green growth, 3) Veraison - Veraison: - Water, sugars, and nitrogen compounds are transported to the berry via the phloem - Sucrose is hydrolyzed to glucose and fructose (Sugars) - Berry flavor and aroma compounds are synthesized within the berry - Berry metabolic activities and composition is influenced by: arrest of phloem transport and onset of dehydration. Optimum time for harvest: when the desirable enological characteristics ceases in the grape berry.
Optimal Maturity - Depends on the style of wine being made. - If clear target exists, harvest is optimized to meet these goals. - Components for assessment of grape maturity - Sugar - Acidity - ph - Berry metabolites: Arginine, Glutathione, Phenolic Content, Anthocyanin Content, Terpene Content, Gycoside-glucose (GG) Precursors - Berry proteins: specific proteins and specific enzymatic activity - Taste: fruit, skins, seeds, stems Balance of Sugar/Acidity
Water status in the plant Plant tissues are ca 80% water. If the plant does not get enough water it emits the transport of the available nutrients from the soil to the fruit, the respiration of water to the atmosphere and dehydration. For this reason irrigation is one of the most important activities for a farm.
20 000 LITERS The amount of water needed to produce one kilogram of cotton: equivalent to a single T-shirt and a pair of jeans.
Chlorophyll - Is a pigment that gives the green color to the stem and the plant. - Chlorophyll is a vital component of photosynthesis, which is how plants get their energy, and how they transform carbon dioxide to oxygen which we breath. - Chlorophyll is a light-absorbing pigment, and it actually gets its green color because it absorbs blue and red wavelengths of light. The green wavelengths are reflected, giving that unmistakable color to plants. - There are two types of chlorophyll: chlorophyll a and chlorophyll b.
THESE PHOTOS WERE TAKEN LESS THAN 10 MINUTES AND 30 FEET APART. PHOTOS: KATIE GRZESIAK. http://www.thoughtandawe.net/biology/plants-without-chlorophyll/
Chlorophyll - Measuring chlorophyll provides valuable information about the physiological status of plants, e.g. plant stress and nitrogen levels. - Low levels of chlorophyll: make the plant turn yellow and decreases glucose (sugar) production and movement in the plant. - Nitrogen levels in plants are a vital component for a good plant health. It is absorbed from the soil and added as a fertilizer during production. Excessive amount of nitrogen in soil leads to pollution.
SUGAR - Sugar is a component often used to assess ripeness. - Sugar content increases during ripening and is therefore a function of berry age. - Several studies have shown no relationship between sugar levels and accumulation of grape berry flavorants (substances which give flavor). - Sugar accumulation can cease due to unfavorable environmental conditions: very high or low temperatures, but resume once the conditions have changed.
SUGAR Initial rapid phase of sugar accumulation, which at some point during berry development and aging, the vine ceases transport of sugar to the fruit.
ACIDITY - Acidity can be evaluated as either ph or titratable acidity, or both. - Historical index: Brix 1. Optimal sugar / acidity balance is achieved if the product of the Brix value times the square of the ph is in the range of 220-260 2. Brix value divided by the titratable acidity: 30-32 - Sugar: Acidity ratio depends on: variety, growing conditions. - Changes in acidity level reflect berry metabolic activities: malate is consumed as an energy source in the berry during veraison
ACIDITY Tracing two different acids: malate levels decrease relative to tartrate.
Phenols - The phenolic content in wine refers to the phenolic compounds (natural phenol and polyphenols) in wine, which include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. - This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids, 90% of phenolic content in wine, include the anthocyanins and tannins which contribute to the color and taste of the wine. - These phenols, mainly derived from the stem, seeds and skin are often leached out of the grape during the period of winemaking. The amount of phenols leached is known as extraction.
Phenolic content - Both the quantity and quality of phenols is important for a good balance. - Some vineyards harvest fruits from each side of the grapevine canopy at different time periods: Why? - Light and temperature have an effect on phenols. Vineyard orientation effect. - Heat and light interception can have an important influence on fruit chemistry - Difference in skin tannin per berry (phenolic compound) - Skin pigment components: skin color and small polymeric pigments in the skins - These changes have been noted in the absence of difference in degrees Brix.
Phenols: Tannins - Grape and wine tannins are composed of subgroups (flavon-3-ols). Those tannins which contain fewer than five subgroups are predominantly bitter and contribute to tannin hardness. - Those tannins which contain more than five are predominantly astringent (dry) and contribute to suppleness (soft, lush wine). - As grape skins mature, the average number of subunits in the tannins increases, increasing tannin suppleness. This is an important sensory and maturity feature. - Mature tannins in the fruit are a requirement for premium red wines and, therefore, are an important harvest consideration. If the skin contains nonpolymerized, harsh tannins, so will the wine.
Phenols: Anthocyanins - Pigments, belonging to the flavonoid group of phenols and contribute to colours such as red, purple and blue. - Occur in the whole plant: roots, stems, leaves, flower and fruits. - Significant attributes of the final product: red wine. - Anthocyanins do not affect the taste of wine, but they do interact with some of aroma substances and can influence wine flavour. - They have a positive influence on human health, antioxidants, anticancer etc..
Natural mutation
Phenols: Anthocyanins - There are numerous anthocyanin compounds in fruits. Most of fruits have a major pigment, which can be used as an indicator of the whole anthocyanin concentration. - Chlorophyll and Anthocyanins: fruit matures from green to red. - Wine quality depends to a degree on tannin / anthocyanin ratio, as the anthocyanins and tannin molecules bind to each other. A process called polymerization. - This ratio impacts color, color stability and mouthfeel
Measuring fruit maturity by the use of imaging and spectroscopy
Applying imaging and spectroscopy to fruit maturity - They are non-destructive methods which enable the acquisition of fruits internal quality parameters without damaging their surface. - The measurement process are simple and rapid, as no complex pre treatments or chemical reactions on fruit samples are needed. - They enable the detection of several fruit internal attributes simultaneously. - Applied to: analyze firmness, color, damage, pests, plant stress etc..
Color 675 nm 750 nm 800 nm 900 nm 980 nm 50-60%, 70-80%, Full-ripe
Challenges - Variety differences - Different leaf stages of growth need specific calibrations - The atmosphere around: e.g. weather, sun etc. can have an influence - Different fruit - different needs - Cost too high - > until now - Different spectra, hard to capture all components - Individuate all spectral components - Depending on what are you capturing, inside, only skin etc.
Grower Perspective: Raspberries and Grapes - What are the common quality attributes? - What are the differences between them? - What could the grower gain from tracing ripeness and quality?
Questions?