| Lemon is a typical tropical cash crop.The harvested area of lemons in China is over 1.5 million mu.Total lemon production accounts for 13% of the world's total production.Hainan lime and perfume lemon are the dominant varieties.Whole island have regular planting.It has been rated as a national geographical indication product.and has become a “precise poverty alleviation” industry.It is an important way for farmers to increase their income.At present,due to the lack of processing technology,low comprehensive utilization efficiency,and low added value of products,it seriously affects the healthy development of the lemon industry.This paper uses Hainan lime and perfume lemon as raw materials to carry out research and development of key products such as freeze-dried fruit pieces,fermented fruits and essential oils,and supporting processing,providing necessary technical support for industrial development.The research results are as follows:1.Freeze-dried lemon slices were developed using vacuum freeze drying technology.(1)The effects of pre-freezing time,first-stage freeze-drying time and second-stage freeze-drying temperature on the water content,rehydration rate and VC content of freeze-dried lemon slices were determined by single factor experiments.The optimal process combination of freeze-dried lemon slices was obtained by orthogonal experimental design.The best process for vacuum freeze-drying of Hainan lemon is 7h for pre-freezing time,5h for the first stage,and 70 h for the second stage.The lyophilized lemon slice has a VC content of 103.86 mg·100 g-1,a water content of 1.35%,and a rehydration rate of 72.84.(2)The comparison of the physical and chemical indicators of the lemon slices obtained in this experiment with the other four commercially available dried lemon slices shows that the comprehensive index of A lemon slices is better than the other four dried lemon slices.The water content was 2.7%,the rehydration rate was 81.03%,the vitamin C content was 101.98 mg·100 g-1,the total acid content was 109.45 g/kg,and the reducing sugar content was 15.88 g/100 g.The sensory score was: D>A>B>C>E,and the optimized freeze-dried lemon slices were of good quality.Using gas chromatography-mass spectrometry(GC-MS)to identify the components of five dried lemon slices,it was found that 100 volatile aroma components were identified in five dried lemon slices.Among them,olefins(51 species)and alcohols(22 species)are the most abundant compounds,and among all aroma components,D-limonene has the highest relative content,accounting for about 10%-30% of the total content.2.The fermented lemon was developed using the traditional method of pickling in Hainan.(1)On the basis of the single factor test,the Box-Behnken Center was used to design a 4-factor 3-level response surface test.The optimum technological conditions for the fermentation conditions of Hainan lime fermentation were: 3.93 min,the cooking time was 7.43 min,the salt content was 39.99%,the pickling time was 16.10 d,and the sensory evaluation score was 69.1349.(2)In the five stages of pickling in the early stage of lemon,the total acid content showed a downward trend,and the content of reducing sugar and nitrite increased first and then decreased.The monitoring results of nitrite content in the fermentation process were lower than the limit of 20 mg/kg,and the content of soluble solids also increased gradually with the prolongation of fermentation time.A total of 74 volatile organic compounds were identified in five different stages of fermented lemon.38,37,34,43,and 32 species were identified in five stages.From the relative content,the relative content of d-limonene,terpinene,myrcene and o-isopropyltoluene is relatively high.3.Lemon essential oil was extracted by ultrasonic assisted steam distillation.(1)The ratio of material to liquid,ultrasonic time and distillation time are single factors.Based on the evaluation index of essential oil yield,a three-factor,three-level response surface test was designed using the Box-Behnken Center combination.The optimum process conditions for Hainan lime oil are: The ratio of material to liquid was 1:14,the ultrasonic time was 51 min,and the distillation time was 8 h.The yield of essential oil obtained by using this process parameter was 2.09%.(2)GC-MS analysis of lemon essential oil showed that 35 kinds of chemical components were identified in the four lemon essential oils,including compounds such as alkenes,alcohols,ketones and aldehydes.Limonene is the main substance of volatile aroma components,and its relative mass fractions are 69.112%,73.318%,65.365% and 66.512%,respectively. |
PDF Full Text Request