The compounds that the grape berry produces to protect the seeds are "organic acids, tannins, and pyrazines" -- and those compounds "combine to make foraging by birds and mammals a downright unpleasant experience" (www.practicalwinery.com). The grape's seed is in fact created during the first "period of growth" (when the berry is hard and bitter tasting); during the second period of growth the goal of the fruit is to "make the berry as appealing as possible to birds and mammals so that seed dispersal can occur" (Practical Winery). The University of California Agricultural and Natural Resources Website reports that a grape berry becomes fruit after "successful pollination and fertilization and the initiation of seed development" (p. 31).

How do humans interfere in this process by consuming grains and fruits?

Assuming this question refers to the consumption of a fruit, such as a concord grape, by a human, certainly there will not be seed dispersal when the seeds work through the digestive system and into a facility that breaks down raw sewage for sanitary purposes.

Does the seed use the fructose or starch in fruits for its metabolism?

In the immature green tomato seed, a fruit, after a period of "transient...

As the fruit develops, the "suc synthase, fructokinase…and soluble and insoluble starch synthases" tend to decline dramatically in concert with the decrease in the starch levels. In other words, in the tomato seed, both the sucrose and starch play important roles in metabolism (Schaffer, et al., 1997, p. 739).
Works Cited

Dokoozlian, Nick K. (2007). Grape Berry Growth and Development. University of California

Agriculture and Natural Resources. Retrieved February 16, 2011, from http://www.ucanr.org/sites/intivit/files/24467.pdf.

Gemini Geek. (2009). Why Are Some Fruits Sweet While Others Are Sour? Retrieved February

17, 2011, from http://www.thegeminigeek.com/why-are-some-fruits-sweet-while-others-are-sour/.

Kennedy, James. (2002). Understanding Grape Berry Development. Practical Winery and Vineyard. Retrieved February 16, 2011, from www.practicalwinery.com.

Schaffer, Arthur a., and Petreikov, Marina. (1997). Sucrose-to-Starch Metabolism in Tomato

Fruit Undergoing Transient Starch Accumulation. Plant Physiology, Vol. 113, 739-746.