Introduction

Ammonium oxalate (also known as ammonium oxalate monohydrate) is a weakly alkaline ammonium salt (Figure 1). The oxalate ion in its structure has a strong metal chelating effect, which can extract water-insoluble pectin formed by chelation with calcium ions in plant cell walls. In addition, the pollution of ammonium oxalate to the environment is much lower than that of strong acids and bases, and the corrosion of equipment in actual production is much lower than that of traditional acid methods. This article lists some research reports on the process of extracting pectin by ammonium oxalate method.

Extraction Pectin from Red-heart Kiwifruit Peel

Red-heart kiwifruit as raw material, using ammonium oxalate as an extraction solvent, pectin was extracted from red-heart kiwifruit peel. Optimized by single factor experiment and orthogonal experiment, defined the optimum process conditions for extracting pectin. Results found that all factors have an influence on extracted ration rate of kiwifruit peel pectin, such as, ammonium oxalate mass concentration, extraction temperature, extraction time, solid-liquid ratio. The best extraction condition is: ammonium oxalate mass concentration was 1.5%, extraction temperature was 80 ℃, extraction time was 3.0h, solid-liquid ratio under 25:1. Under the optimal process conditions, the extraction rate of pectin reached up to 12.95%. [1]

Extraction Pectin from Wax Gourd Peel

LI Ying et al. had studied the extraction of pectin with ammonium oxalate from wax gourd peel. Ammonium oxalate extraction process was optimized by orthogonal array design on the basis of a series of single-factor experiments, and physicochemical property of pectin from wax gourd peel were determined. The results showed that, ammonium oxalate concentration, temperature, extraction time and material-to-liquid ratio could affect pectin extraction differently. And the optimal conditions of the four parameters were 1.5 %, 80 ℃, 2.0 h, and 1:30 (g/mL), respectively. Under these conditions, the extraction rate of pectin reached up to 8.91 %. Furthermore,the quality indicators of the extracted pectin could meet the requirements of the government standard (GB25533-2010) and the industrial standard (QB 2484-2000).[2] Ammonium oxalate method not only has the advantages of simple process operation and environmental friendliness, but also has the advantages of short experimental time, low cost, and high extraction rate, etc.

Extraction Pectin from Okra

The extraction process for pectin from okra, using ammonium oxalate as the extraction solvent combined with microwave-assisted, was optimized by single factor experiment and orthogonal experiment, and then the pectin quality was analyzed. The optimum conditions were as follows: solid-liquid ratio of 1:20 (g/mL), amount of ammonium oxalate 13 g/L, microwave power mid-range (60% × 800W), and microwave radiation time 20 min. Under these conditions, the extraction yield of pectin was 23.64%.[3] Wu Zhanxia et al. extracted pectin from Okra using ammonium oxalate combined with microwave-assisted method. Results were reported as follows: okra solid-liquid ratio is 1:10, ultrasonic temperature is 80 ℃, ultrasonic power is 400 W, ultrasonic time is 50 min, oxalate percentage concentration is 1.4 %, the extraction of the best extraction rate is 24.32 %. The quality indicators of the extracted pectin could meet the requirements of the industrial standard.[4]

Extraction Pectin from orange peel

Using orange peel as raw material, the pectin was extracted by ultrasonic assisted ammonium oxalate method, and the effects of ammonium oxalate concentration, liquid-solid ratio, ultrasonic time, and extraction temperature on pectin extraction rate were studied by single factor and orthogonal experiment.The results showed that the optimal extraction conditions were as follows: ammonium oxalate concentration 0.75 %, solid-liquid ratio 1:21 (g/mL), ultrasonic treatment time 50min, extraction temperature 85 ℃. Under these conditions,the extraction yield of pectin reached 21.42%. This study provided theoretical basis for the industrial production of orange peel pectin extraction.

In summary, these studies can provide theoretical references for the extraction of pectin from various fruit peels, and further expand the application of ultrasound/microwave-assisted ammonium oxalate method in pectin extraction.

References

[1]Jiang Zhiwei et al. Study on Extraction Pectin of Red-heart Kiwifruit Peel by Ammonium Oxalate[J]. Anhui Agricultural Science Bulletin, 2019,25(16):122-124.

[2]LI Ying et al. Ammonium Oxalate Extraction and Analysis of Physicochemical Property of Pectin from Wax Gourd Peel[J].Food Research And Development,2017,38(20):47-50.

[3]Huang Ziqi et al. Study on the Process of Extracting Pectin from Okra with Microwave-assisted Ammonium Oxalate[J].Guangzhou Chemical Industry,2015,43(17):77-79+113.

[4]Wu Zhanxia et al. Ultrasonic Assisted Ammonium Oxalate Extraction Okra Pectin[J].Guangdong Chemical Industry,2016,43(07):31-32+10.