Analysis of the production process of preserved fruits and candied fruits

Most varieties of fruits and some vegetables can be used to make preserved fruits.Due to differences in texture,moisture content,and organic acid content,various fruits have different processing methods and conditions,but the overall process flow is nothing more than:

1、Raw material selection

The basic principle of fruit preservation is to use the high osmotic pressure of high concentration sugar solution to extract excess water from the fruit,absorb suitable sugar on the surface and inside of the fruit,form a high osmotic pressure,inhibit the survival of various microorganisms,and achieve the purpose of preservation.According to this principle,when making preserved fruits,attention should be paid to selecting varieties with low water content and high solid content,varieties with beautiful color,delicate flesh,and toughness,varieties with good storage and transportation resistance,and varieties with easy detachment of fruit cores.

2、Pre processing

Various fruits have different textures and organizational structures,and different methods and measures should be taken during processing.For example,before processing dried dates,the skin should be evenly striped to accelerate the penetration of sugar solution;For example,preserved apricots and other fruits should undergo sulfur fumigation treatment before processing.Fruits treated with sulfur fumigation can not only avoid or reduce oxidative browning during the drying process,but also reduce the loss of vitamin C in the fruit.According to experiments,the vitamin C content of prickly pear dried with sulfur fumigation is at least 25.84%higher than that of the control group without sulfur fumigation,and the highest is 58.34%.For example,before processing dried peach and apple,mechanical peeling,artificial peeling,or chemical peeling treatment are used.

3、Preparation of sugar solution

The moisture content of normal dried fruit products is 17-19%,and the total sugar content is 68-72%.Among them,the reducing sugar content is 43%,accounting for more than 60%of the total sugar content.When the sugar content is above 60%,there will be no"sand return"(sucrose crystallization occurs on the surface or inside of the finished product)or"sugar return"(glucose crystallization occurs on the finished product)phenomenon,and the product quality is the best.When the reducing sugar content is 30%,accounting for less than 50%of the total sugar,the finished product will experience varying degrees of sand return after drying.Dried fruit that returns sand loses its normal luster and is prone to damage,seriously affecting the appearance and quality of the finished product;When the content of reducing sugar is between 30%and 40%,although the finished product does not return to sand temporarily after production,slight sand return may still occur during storage,and the degree of sand return will decrease with the increase of reducing sugar content;When the content of reducing sugar is too high,it is easy to experience the phenomenon of"sugar return"in hot and humid seasons.From this,it can be seen that the ratio of sucrose to reducing sugar in dried fruit products determines the quality of the products,and the main source of sugar in the products is sugar solution.Therefore,the preparation of sugar solution is actually the key technology in dried fruit production and must be highly valued.Experience has shown that the sugar solution used to cook preserved fruits,especially those containing less organic acid such as apples,should be supplemented with a certain amount of organic acid during the cooking process,and its pH value should be adjusted to control the proportion of reducing sugars in the sugar solution.In practice,it has been found that when the pH value of the sugar solution is adjusted to 2-2.5,after 90 minutes of cooking,most of the sucrose can be converted,and the product quality can be guaranteed.

4、Cooking and impregnation

The cooking and soaking methods of various preserved fruits can be basically divided into two types:

(l)One time cooking method is mainly used for processing fruits with low water content,large cell gaps,and loose tissue structure,such as apples,dates,and so on.The specific cooking and soaking times should be determined separately based on the variety.However,the production of preserved fruits in certain southern regions is slightly different from that in Beijing.For example,preserved fruits such as peach slices and plum slices made in Fujian are peeled,peeled,and pitted before being soaked in 0.2%lime water,then blanched and sugar soaked,and produced using a one-time cooking method.

(2)The multiple cooking method is suitable for fruits with high water content,thick cells,dense tissue structure,and easy rotting during the cooking process.Because the fruit is cooked and soaked in one go,not only is it difficult for the sugar solution to penetrate into the interior of the fruit,but it is also prone to rotting and even cooking the resulting sauce.Therefore,the method of multiple cooking and soaking is adopted.For example,peaches,pears,apricots,etc.are processed using multiple cooking methods.Some pears are not easy to cook,but due to their high water content,the sugar content is difficult to penetrate into the interior.During the cooking process,a large amount of water in the fruit seeps out and dilutes the sugar concentration under the soaking of sugar.If the cooking time is extended,it will inevitably increase the cost,so multiple cooking methods are generally adopted.In addition,the multiple cooking method can also cause the protein cells and protoplasm in the fruit to solidify under heat,resulting in better permeability.At the same time,it also uses heat to destroy various enzymes in the fruit,which is conducive to preventing tannin oxidation and browning,and maintaining the delicious color of the fruit.

5、Dehydration drying

Dehydration and drying is the final process in the production of preserved fruits,with the aim of removing excess water from the fruit,forming a layer of"sugar coating"on the surface of the product,inhibiting the survival of microorganisms in various places,and achieving the goal of long-term preservation.Due to the differences in dried fruit products,the degree and time of drying also vary.