I read this in Science Daily. Apparently you can get 2-9 F degrees of protection. Here is a link to the full article of the selection from below from Science Daily.
"A report published in HortTechnology premiered the novel topical spray developed to increase resistance to both cold damage and cold mortality in plant foliage, flowers, and fruits. According to David Francko, Dean of the Graduate School and Professor of Biology at the University of Alabama, the patent-pending formula has been commercialized under the trade name FreezePruf.
The spray is composed of ingredients that are non-toxic to plants, humans, and animals. "The components of the laboratory spray formulation and FreezePruf are all either human food ingredients or used in the human food production chain," said Francko. He said that the spray actually improves plants' natural ability to tolerate freezing conditions.
The researchers tested the spray on a wide variety of foliage, flowers, and fruits. Data showed that both the laboratory formulation and the commercial version of the spray decreased the first damage temperature and the mortality temperature of the plants. "We noted beneficial effects within hours of application," Francko remarked. "Our results suggested that the spray formulation could add the equivalent of approximately 0.25 to almost 1.0 USDA Plant Hardiness Zone to the cold hardiness rating of the plants used in the experiments."
Here is a link to FreezePruf information http://pro.liquidfence.com/ecologic/freeze-pruf.html