Abstract: Methods are provided for processing and dispersing animal tissues that involve exposing processed (e.g., decellularized) tissue to an acylating agent, wherein the ratio of acylating agent to wet tissue weight is about 0.003:1 or less. Preferably, decellularized tissue is exposed to an amount of the acylating agent of about 0.1% to about 0.3% of wet tissue weight for a time ranging from about 30 seconds to about 10 minutes. A dispersed tissue matrix is produced that has a high degree of resistance to digestion by non-collagenase proteases, such as trypsin. In order to produce sufficiently high yields of these trypsin-resistant compositions, the processed tissue is preferably cryomilled to increase its surface area prior to acylation. The dispersed acylated decellularized tissue may be in the form of an injectable composition that can be introduced into tissue of a subject.