Lucene.NET HitHighlighter (with Boolean Query) could be used in combination with Sitecore.

GenerateHighlightText.cs

/// <summary>
/// Uses Lucene Contrib Highlighter to create search highlight based on an index field/string with all content
/// This code requires Lucene 3.0.3.0 DLL from Nuget and is not supported with the Sitecore7 Lucene DLL out of the box.
/// This is pure Lucene code and does not use any Sitecore namespaces.
/// Adding Try/catch is advised. searchQuery = searchterm/keyword(s)
/// </summary>
private string GenerateHighlightText(string pageContent, string searchQuery)
{
	var analyzer = new StandardAnalyzer(Lucene.Net.Util.Version.LUCENE_30);
	// Create Wildcard query using the BooleanQuery for multiple words.
	var booleanQuery = new BooleanQuery();
	var segments = searchQuery.ToLower().Split(new[] { " " }, StringSplitOptions.RemoveEmptyEntries);
	foreach (var segment in segments)
	{
		var wildcardQuery = new WildcardQuery(new Lucene.Net.Index.Term("", segment + "*"));
		booleanQuery.Add(new BooleanClause(wildcardQuery, Occur.SHOULD));
	}

	IFormatter formatter = new SimpleHTMLFormatter("<strong>", "</strong>");

	// set max size for every segment
	var fragmenter = new SimpleFragmenter(132);
	var scorer = new QueryScorer(booleanQuery);
	var highlighter = new Highlighter(formatter, scorer) { TextFragmenter = fragmenter };

	// remove html tags from content
	string rawPageContent = StringUtil.RemoveTags(pageContent);

	// get highlighted fragments
	TokenStream stream = analyzer.TokenStream("", new StringReader(rawPageContent));
	string highlightedFragment = highlighter.GetBestFragments(stream, rawPageContent, 3, "...");
	if (!string.IsNullOrWhiteSpace(highlightedFragment))
	{
		return new HtmlString(highlightedFragment);
	}
}