I want to show the 5 words before and after "nutrient":

... The aforementioned oxygenated *nutrient* emulsion (using the fluorocarbon FC-80) ...

   <xsl:template match="z:e">
       <xsl:value-of select="preceding-sibling::text()" />
       <b>
           <xsl:value-of select="." />
       </b>
       <xsl:value-of select="following-sibling::text()" />
   </xsl:template>

Cheers,
-- Abel Braaksma