Some ‘juicy’ research on nutrition

A study by researchers at the Texas A&M University College of Agriculture and Life Sciences has shown the choice of household juicing technique can affect the healthful qualities of common vegetable juices.

The results of this research were recently published in the ACS Food Science & Technology publication of the American Chemical Society. 

“Home juicing machines have become popular in recent years, but juicing can alter the levels of health-promoting bioactive compounds and antioxidants in raw vegetables by exposing the inner tissues to oxygen, light and heat, and by releasing enzymes,” said study lead Bhimu Patil, Ph.D., a Texas A&M AgriLife Research scientist and director of Texas A&M’s Vegetable and Fruit Improvement Center, or VFIC.

In the study, Patil, along with graduate student Junyi Wang and G.K. Jayaprakasha, Ph.D., AgriLife Research scientist at the VFIC within the Department of Horticultural Sciences, compared levels of health-promoting bioactives and antioxidants in vegetable juices created by blending, high-speed centrifugal juicing or low-speed juicing. The study received funding from the U.S. Department of Agriculture-Specialty Crop Research Initiative.

“Consumers have different types of juicers to choose from, but there is limited information on which type of juicer best retains the healthful components of the fruits and vegetables being processed,” Patil said. “The objective of our research was to find out what juicing technique might best maintain the nutritional value of the variety of vegetables chosen for the study.”    

Patil said while there was no “clear winner” as a juicing technique, the study demonstrated what technique would work best for each type of vegetable chosen for the study in order to maintain their beneficial nutritional compounds.  

Three methods, 19 vegetables compared        

One of the three juicing techniques used was blending, which crushes vegetables with fast, spinning blades, typically resulting in a thick juice with a lot of dietary fiber. It also produces a good deal of heat as the vegetables are blended.

The second technique, high-speed centrifugal juicing, quickly pulverizes vegetables and separates out pulp and fiber, making for a thinner juice.

The third, low-speed juice extraction, squeezes juice with a horizontal auger that rotates at a low speed, producing the least heat of the three methods, but also removing pulp and fiber.

Nineteen vegetables of different varieties, production systems and colors were purchased from local supermarkets for the study. They included white, yellow and green cauliflowers; green, green organic and red organic kale; purple-white and white baby turnips; red, green and white radishes; red, red organic, golden and golden organic beets; and orange, purple, yellow and white baby carrots.

Phytochemicals present in processed vegetable juices were monitored and identified. Color attributes and antioxidant activities of the processed juices were also determined.

“We identified 85 different metabolites, including kaempherol, quercetin glycosides and amino-acid attached betaxanathins as potential markers for the differentiation of processing techniques,” Patil said.

Pulp facts, not pulp fiction

After preparing juices with the different methods, the researchers observed that, in general, blending produced juices with the lowest amounts of beneficial compounds such as vitamin C, antioxidants and phenolics, probably because the technique produced the most heat.

“Low-speed juicing generated the highest amounts, although exceptions were found for certain vegetables,” Patil said. “However, likely because of their higher fiber content, blended vegetable juices had the highest amounts of α-amylase inhibitors, which could help reduce hyperglycemia after a meal.”

He said the results showed the low-speed juicer produced more diverse metabolites than the other two methods, but the relative abundances for the three juicing methods differed based on the type of vegetable.

“What we determined was that consumers should increase their consumption of fruits and vegetables by using blenders to produce smoothie-type beverages with high fiber contents and low-speed juicers to produce juices with high antioxidant contents,” Patil said. “High fruit and vegetable consumption can decrease the risk of chronic diseases, so we are happy that our results support diverse, tasty ways to enjoy the health-promoting properties of juicing.”