The main pigments in citrus are chlorophyll, carotenoids and anthocyanins. Chlorophyll is the reason why young fruits appear green. Carotenoids are yellow or even red, and are the pigments that change the color of citrus into orange, red and other mature colors. Anthocyanin is a ubiquitous pigment that is responsible for the various colors of grapes, cherries, apples, peaches, etc.
As citrus matures, chlorophyll gradually decomposes, and the unique background color appears, and the inherent mature color (orange, red, etc.) appears on the background color. This is the internal reason for the color change of citrus. .
1. What affects the coloring of citrus
Both anthocyanins and carotenoids are sugar metabolites, and their content is directly proportional to the total sugar content. When citrus Coloring can only occur when the sugar content reaches a certain concentration. As the sugar content increases, the coloring becomes darker.
1. The outer fruit has a better color than the inner fruit, and the sunny side is darker than the backlit side. Generally, the color of fruits is darker than that of bagged fruits, but for both bagged fruits, the color of the fruits in the bag with excellent transparency is better developed, which shows that light and coloring are closely related.
2. Light energy helps to increase pigments. On the one hand, it promotes photosynthesis of leaves and allows more sugar to flow into the fruit. On the other hand, light may directly induce the formation of pigments.
3. Appropriate low temperature can increase the synthesis of anthocyanins and carotenoids.
4. Too much nitrogen will result in poor coloring. Excessive nitrogen is conducive to the formation of chlorophyll, promotes branch growth, promotes the formation of a large amount of amino acids and proteins, increases the consumption of organic matter, and reduces the transfer of sugar into the fruit.
2. What affects the sweetness of citrus fruits?
1. Different varieties have different sugar levels when mature. Only by using grafting and seedling cultivation methods to establish orchards can citrus varieties have the same sweetness genetics. Stable; at the same time, the rootstock combination also affects the sweetness of the fruit.
2. Fruits mainly contain fructose, glucose and sucrose; fructose is the sweetest, followed by sucrose and glucose. Citrus mainly contains sucrose.
3. The sweetness of citrus is not only related to the type and content of sugar, but also related to the type and proportion of acid (tartaric acid, malic acid, citric acid, etc.). The temperature affects Supports the respiratory degradation of acids contained in citrus.
4. Citrus mainly contains citric acid, and its respiratory degradation temperature is higher than that of tartaric acid and malic acid. Therefore, the temperature before and after the ripening of citrus in autumn and winter is directly related to the speed of respiratory degradation of citric acid, which affects the sugar in the juice. The rate at which the acid ratio increases shows the difference in sweetness of citrus fruits in different years.
5. The sweetness of citrus fruits is closely related to the leaf-to-fruit ratio; the leaf-to-fruit ratio is moderate, the vegetative growth of branches and leaves is coordinated with the reproductive growth, the effective photosynthetic duration is maintained, the photosynthetic intensity is high, and starch synthesis, transportation, distribution and accumulation are greater than organ construction. The consumption is beneficial to converting into sugar and increasing the sweetness in the juice.
6. The sweetness of citrus fruits is closely related to the orchard soil conditions and fertilization. All orchard soils have deep effective soil layers and high organic matter content. Fertilization is mainly based on organic fertilizers all year round. The proportion of nitrogen, phosphorus, potassium and various trace elements in the fertilizers is appropriate. The year-round supply of fertilizer and water to the tree body is timely and stable, and the vegetative and reproductive growth of the fruit trees are ensured. Coordinated, the fruits are large and have a rich and sweet flavor.
3. How to improve the coloring and sweetness of citrus
1. Deep plowing and applying organic fertilizer, interplanting green manure, and adding biological fertilizer to improve the soil. The use of dry cake, peanut bran and bio-organic fertilizers is advocated.
2. The orange orchard should be changed from dense to sparse, and the tree crown should be changed from high to short to ensure the formation of an "independent tree". Tree pruning should follow the principle of ventilation and light transmission. Control water 20 to 30 days before harvesting, and use reflective film to cover the ground, which not only controls water but also provides light, which is beneficial to increasing the sugar content of the fruit.
3. Phosphorus can improve the fertilizer absorption capacity of fruit tree roots, drought and cold resistance, promote flower bud differentiation, improve fruit quality and increase fruit yield;
4. Potassium can promote branch growth. Thick growth, developed mechanical organization, improved cold resistance, drought resistance, disease and pest resistance, and improved fruit yield and storage performance.
5. If the soil is deficient in zinc, boron or magnesium, foliar fertilizers of zinc, boron and magnesium should be applied.